"stuck" in Viet Nam: what IS this pesky sediment?

lsemprini

Member
Jul 13, 2021
6
Hoi An, Viet Nam
Hi all and thanks in advance for helpful advice.

Thanks to COVID I am "stuck" in Hoi An, Viet Nam (good place to be stuck) and as the only tenant in a 6-apartment building (a typical scene as tourism is decimated here) I have taken on the role of maintaining (and enjoying) its pool. Thanks to this forum and many YouTube resources I have given myself a crash course in pool maintenance that has been mostly successful.

After an initial chlorine shock and nursing the 28728L (7589G) pool from green back to blue 2.5 months ago, I have been very diligent about measuring and maintaining proper pH/Chlorine/Alkalinity levels, skimming leaves and stuff off the pool surface daily, brushing and vacuming the pool every few days, and backwashing the sand filter regularly (trying backwash intervals ranging from daily to every 2 weeks).

BUT despite all that, the pool consistently has this sediment floating in it (see video here and pic attached below):

(video showing symptom)

IMG-20210709-224321 (full-res image)

Even if I run my pump for 24 hours, the sediment remains. If I vacume to filter, no change. If I sweep, vacume to waste, and backwash, the sediment is back in 1 day just the same.

The sediment is all over the pool, but particularly noticeable in the pool light at night. The sediment is lighter than beach sand (I don't know what kind of sand is inside the filter), moves very slowly, and takes hours and hours to settle. But other than this sediment, the water is NOT cloudy and stays blue.

I have tried mega-shocking the pool again (bringing the Chlorine level to where OTO turns bright red (>35ppm TC Is there a basic test kit with distinctive yellow colors? ) and bright orange (>25ppm TC) for several days ) and it didn't help.

WTF is this sediment and how do I get rid of it? See theories below.

In addition to the sediment, there is one more suspicious symptom. If I gently drop the pool brush to the bottom and make a quick stroke, I can always see a very subtle cloud of greyish fine dust. It is hard to see even with a still pool, but it is always there. But that dust never rises and the pool itself is never cloudy and stays blue. More on that later...

Vital stats:
  • Volume: 28728L (7589G)
  • Design: infinity edge (see pic) with tile walls and floor
  • Circulation: not fantastic: intake jets are at bottom of pool at shallow end and middle of pool, main drain at deep end, infinity edge that is installed incorrectly so that it only spills at shallow end (so not great circulation from jets to deep end)
  • Placement: pool is mostly covered under a roof (about 10% of it gets sun during the day but I cover that part with a plastic tarp, and that vastly reduces Chlorine consumption too) in a hot beach town in Viet Nam where the air temp ranges from 90F - 103F every day, and where the sea wind is always carrying pollen and other stuff to the pool surface. Water temp roughly ranges 77 F - 85 F (pool is in shade).
  • Chlorine: ALL chlorine (both shocking and everyday) comes from 70% cal hypo granules. The pool eats approximately 42g of cal hypo per day in order to stay level (though it depends on temp). Liquid chlorine never used. I use an OTO test and keep the TC between 1ppm and 3ppm as best as the test allows (* see important note below about FAS-DPD/FC test availability). After the initial balance on pool startup, whenever I add Chlorine, the TC jumps very predictably from the amount I added, so this indirectly suggests that the TC in the pool is mostly FC.
  • pH balancing: after initial pool startup and balance (when I used some baking soda and soda ash to establish initial alkalinity and pH), I only ever need to reduce the pH (the sun and aeration raise the pH every day), and I do so with small amounts of Muriatic Acid (200ml per week approx). I keep pH in range 7.6-8.2. I am using a good-enough electronic Chinese pH meter that I calibrated with real distilled water from a local water safety university and 3 pH buffer powders.
  • CYA: There is NO cyanuric acid in the water and never has been. This pool never used dichlor, trichlor or any other tablets. I am happy about this; the stuff seems like a a nightmare and cal hypo is cheap and plentiful.
  • Alkalinity: I initially got the Alkalinity to roughly 80 and I believe it may have oozed down to 60 by now, but I can only measure alkalinity using a really ****** Chinese test strip where the strip color barely resembles any of the example legend colors ( * see important note below about test availability)
  • Calcium Hardness: The only tool I have to measure this (****** Chinese test strip) sucks, sucks, sucks. The color doesn't match any of the legend colors, even when the Chlorine and pH are in a good range. If I had to guess, I would guess 250-500, but the color match is absurd. Since I use cal hypo, wouldn't one expect high calcium hardness?
  • Pump: sand filter. Doesn't matter how long I run the pump, the sediment remains. I typically run it for 2-3 hours per day but even at 24 hours the sediment remains.
(*) IMPORTANT NOTE ABOUT TEST AVAILABILITY: I KNOW I should use the Taylor K2006 with its great FAS-DPD test, reverse titration, and BELIEVE ME I WANT ONE but it is SIMPLY NOT AVAILABLE in Viet Nam. I've looked and looked and looked. Even Viet Nam websites that clam to sell it NEVER have it. If I got a friend to ship a kit, not only would it cost >$70 in shipping alone, and not only would it take >30days to arrive thanks to COVID even with "express" USPS service, but there's a 75% chance that Viet Nam customs would steal it or it would get lost. It's just not an option, sorry. I know it's hard for you to help me if I cannot get the best tests, but it's what I have. Every Vietnamese "professional" pool guy here uses a TERRIBLE test kit with only OTO and a virtually meaningless pH phenol red test, and almost none of these so-called "experts" ever even measure Alkalinity, let alone hardness or CYA or anything else. It's shocking! I can't believe more people don't die in pools here. And there are no other FAS-DPD tests either, not even from China. So I have no way of measuring FC except a super-crappy Chinese test strip whose FC colors never resemble any of the legend colors. Even with the OTO TC test I do use, I had to reverse-engineer the meanings of the colors based on whether my skin itched (UG), since its colors don't resemble the yellow shades on the test container either. Only my pH measurement is really solid.

My theories about the sediment are:

#1 Maybe sand in filter needs replacement? Unlikely because the sand was replaced in the last 2-3 years according to landlord (though maybe the Vietnamese techs here use beach sand :| )

#2 Maybe sand filter laterals/standpipe are damaged and the sediment itself is actually sand? But would sand float as seen in the video (I'm not sure because I've never actually seen filter sand before, nor do I know if they used real filter sand)? And I never see islands of sand at the bottom of the pool.

#3 Maybe sand filter laterals/standpipe are damaged and the sediment itself is junk from the pool? More likely. But then why would I only have large sediment as seen in the video? Why wouldn't my pool be cloudy with smaller particles as well?

#4 Some kind of chlorine-resistant algae like mustard algae? Possible but unlikely since I don't see any stains (though the pool is pattered blue tiles so stains would be a bit hard to see; I don't see any stains on the white ladder stairs), and doing the mega-shock to 35ppm TC didn't affect it. However, the greyish dust mentioned above seems to be a vote in favor of this theory, maybe?

#5 Since I use cal hypo, maybe the sediment is chunks of calcium something-or-other that cannot dissolve in the water because the water is saturated with calcium-something-else already. During pool startup when I used soda ash to raise alkalinity, I totally "snowed out" the pool, with a layer of calcium deposits on the infinity edge thick enough to write on with my finger. But that resolved after a few days. Based on a post in this forum, I tried the trick of taking some of the pool water into a new container, and diluting it a bunch with tap water and waiting 30 minutes. The sediment remained after dilution. So probably not excessive calcium? By the way, while we're talking about calcium, there are three teeny-tiny, sharp spikes of Calcium sticking out at three points in the deep end of the pool (as I understand it, the spiky crystal shapes are more due to insufficient calcium/LSI than the calcium "scale" that is from excessive calcium/LSI but I believe they have been there for much longer than the 2.5 months I've been looking over the pool.

#6 Is my plastic tarp disintegrating into the pool? No, I checked that.

#7 what else??

So so far, #3 seems the best theory? What do you think?

It will be very expensive to get the local guys here to open the pump, possibly replace the sand, and check the laterals/standpipe (because I am a newbie who has never opened a filter, and because the filter is located lower than the pool and thus there is a possibility of an out-of-control spill that empties the pool into an access hole with 240V electrical wires in a country where the breaker is likely miswired and somewhat hot even when off due to ground leaks, I am not confident about performing that operation myself). Based on how disappointed I am with their lack of testing, I'm not even sure if they're capable of checking the laterals. Before I and/or my landlord spend that money, I want to make sure it's sensible to even try that.

Note that clarifier and flocculant are NOT available at all in Viet Nam. Nobody has even heard of either of them here. But I suspect it doesn't matter since the problem is more likely the filter or algae, and even if I did floc to clean, the sediment would come right back.

The only chemicals available in Viet Nam are cal hypo, muratic acid, various dichlor/trichlor Crud, and a few mystery "pool cleaner" chemicals from Thailand which have no ingredients (I can read Thai writing, and there no ingredients in Thai either) and which nobody can tell me what they are.

So, we don't have a the best tools or measurements to work with here, but what can we say from the data so far?

Thanks!
 

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Texas Splash

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Welcome to TFP! :wave: As you adequately noted, you're at a bit of a disadvantage without a proper test kit, so we won't harp on that issue. Here are some of my thoughts after reading your notes:
- I doubt there's a problem with the sand filter itself. If the laterals or center pipe were damaged, you'd have sand under the return jets.
- Cal-Hypo? Well, if that's all you've been using, your CH must be getting up there. We recommend liquid chlorine since it has no ill side effects other than a little salt, but if cal-hypo is all you can get, that's another limitation.
- No CYA; while probably not related to the particulate matter you see floating, no CYA is never good, even for an indoor pool. Chlorine is exponentially strong when not buffered/protected by a minimal amount of stabilizer. For indoor pools we recommend about 20 ppm of CYA to take the edge off of the harshness of the chlorine.
- Have you ever deep cleaned the sand? That might be a good DIY project for you if able.
- No floc or clarifier? GREAT! Those products only cause more problems.

In the end, without precise testing much of what you are experiencing will be guesswork. It would be easy to think of organic matter (algae), and it might be, but with no FAS-DPD to perform an Overnight Chlorine Loss Test there's no way to know for sure. It would also seem unlikely to have an algae problem with the FC so high and no CYA, but again, that's just a guess.

So by doing what you can chemically for now, you might take a look in the filter and/or do a deep clean. Perhaps the sand is compacted or channeled inhibiting your filtration.

 
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cowboycasey

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What a place to be stuck :)

You have done some work here and off to a good start.. Here is what I would do

1. Get some Dichlor or trychlor in there, enough to get 30 CYA and that is it.. add it slowly over days as you do not want to take your Free Chlorine up by 35, 64 oz / 1.8 kg will get you 32 CYA.. PoolMath
1626214643490.png

2. Find DE (diatomaceous Earth), you can add it into your sand filter and it may filter more of what you are seeing out.. Sand Filter Use and Care - Further Reading
Adding a small amount of DE (diatomaceous Earth) can improve the filtering capability of a sand filter. Pool grade DE should be used, food, pet or garden grade will not work.

3. letting some sun hit the water is a great thing, UV burns off Combines Chloramines and since you can not test for CC let some sun/UV hit the pool..

4. since you are always using cal Hypo you may have to empty some water once a year but you already understand and are looking after that.. :)
 

lsemprini

Member
Jul 13, 2021
6
Hoi An, Viet Nam
Welcome to TFP! :wave: As you adequately noted, you're at a bit of a disadvantage without a proper test kit, so we won't harp on that issue.

Appreciated! And thanks for the incredibly useful reply/info. See below...

Here are some of my thoughts after reading your notes:
- I doubt there's a problem with the sand filter itself. If the laterals or center pipe were damaged, you'd have sand under the return jets.
- Cal-Hypo? Well, if that's all you've been using, your CH must be getting up there. We recommend liquid chlorine since it has no ill side effects other than a little salt, but if cal-hypo is all you can get, that's another limitation.

You guessed correctly---I looked all over for either liquid chlorine or household bleach without "flavors" (yes they really call it that on the label) but came up empty. There might be an industrial sodium hypochlorite source in the nearby big city, but I have to wait until after lockdown to try.

- No CYA; while probably not related to the particulate matter you see floating, no CYA is never good, even for an indoor pool. Chlorine is exponentially strong when not buffered/protected by a minimal amount of stabilizer. For indoor pools we recommend about 20 ppm of CYA to take the edge off of the harshness of the chlorine.

OK will look into that. I understand that after adding CYA, the need for chlorine changes drastically. Is there a good guide for that in this site? I am a bit concerned that I will have to add so much cal hypo that it will start causing calcium problems (if I don't have them already)

- Have you ever deep cleaned the sand? That might be a good DIY project for you if able.

No, but thanks for the deep cleaning reference. I read that post and even aside from the deep cleaning, there are some other ideas that are free to try (gently knocking on the side of the filter tank with a rubber mallet, letting backwash run much longer than just when the water goes clear) and some that are easier to try (adding a bit of DE and watching the pressure gauge; not sure if I can get DE here or not but will look). Great to have some new ideas!

As far as whether the filter might be "channeled," a thought occurred...

Some guides to backwashing I saw on the internet suggest backwashing "when the pool pressure is 10 PSI above normal...." but on my pool, the PSI NEVER goes above 5 PSI, and is generally only around 2 PSI during normal operation after a backwash (pump specs shown in attached image).

So does this extremely low pressure indicate something about the filter status? Would a "channeled" filter have a lower pressure?

Actually I'm a bit confused in general about filter pressures---it seems that a really good filter would have a HIGHER pressure since fine filter particles (DE for example) would offer more resistance to flow and better filtering, but at the same time we say to backwash when the pressure goes up (presumably because gunk blocks flow too)...so what actually is the relevance of filter pressure?

In the end, without precise testing much of what you are experiencing will be guesswork. It would be easy to think of organic matter (algae), and it might be, but with no FAS-DPD to perform an Overnight Chlorine Loss Test there's no way to know for sure. It would also seem unlikely to have an algae problem with the FC so high and no CYA, but again, that's just a guess.

One thing I was hoping is by looking at the video and picture of the particles, you experts here might be able to rule out some possibilities based on your experience. For example,
  • by looking at the video can we rule out sand, because sand would always drop immediately?

  • by looking at the video can we rule out algae? Could algae look like that?

  • by looking at the video, could it be undissolved calcium? I mentioned that I tried diluting some water with the particles with tap water and the particles did not dissolve...does that mean the particles are definitely not undissolved calcium?

  • by looking at the video can we figure out anything else about what the particles might actually be?

  • is there some other kind of test/trick I can use to determine what the particles actually are, to narrow down the possible causes?
Thanks!
 

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lsemprini

Member
Jul 13, 2021
6
Hoi An, Viet Nam
What a place to be stuck :)

Yup, it's a nice exile! COVID handling has been very good here so far too.

Thanks for the great tips! See below...

1. Get some Dichlor or trychlor in there, enough to get 30 CYA and that is it.. add it slowly over days as you do not want to take your Free Chlorine up by 35, 64 oz / 1.8 kg will get you 32 CYA.. PoolMath
View attachment 354774

OK. Is there something that can predict how much chlorine I will need after getting CYA to 30? I am a bit concerned that the increased need for chlorine might lead to calcium problems (since I only have cal hypo and sodium hypochlorite is not available here, neither in industrial form nor in the form of household bleach--ALL the household bleach products here have "flavors" (and yes they call it that on the label!)).

2. Find DE (diatomaceous Earth), you can add it into your sand filter and it may filter more of what you are seeing out.. Sand Filter Use and Care - Further Reading

Interesting, thanks. Will see if anyone sells DE here.

3. letting some sun hit the water is a great thing, UV burns off Combines Chloramines and since you can not test for CC let some sun/UV hit the pool..

OK. Currently, even with my tarp, there is a strip about 1-2 feet long where the sun gets in most days.

4. since you are always using cal Hypo you may have to empty some water once a year but you already understand and are looking after that.. :)

Yes...does the video look like it might be undissolved calcium? Are there any other tests I can do to check that? As I mentioned, I tried diluting the particles with lots of tap water and they did not dissolve, so I think that suggests they are not undissolved calcium.
 

cowboycasey

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The particles you are seeing are just that.. little tiny things that a sand filter will not catch.. Sand filters are the easiest filter to use and the worst out of all of them for catching really small stuff.. the stuff you are seeing in the lights is really tiny stuff.. DE is really your only hope to get rid of those particles that the light is showing you..

As for how much more cal hypo I am not sure.. You could try 32 oz dichlor and have 15 CYA in there.. it is just enouph to buffer the chlorine so it is not so intense for you and others in the pool but you are correct, you may have to use a little more cal hypo than you are using now..

this is for dichlor with 0 cya
1626258005574.png

this is trychlor with 0 cya
1626258044147.png

This is cal hypo 73% with 0 cya
1626258104445.png

this is Cal hypo with 30 CYA/64 oz of dichlor.. it is still 2.8 oz so you can still use the same amount but the CYA will buffer the chlorine... you may have to take your FC to 5 daily and that would up your Cal hypo a little bit but not enough to worry about it.. Chlorine / CYA Chart - Trouble Free Pool

1626258367108.png

Your best bet for the particles is the DE, you will get rid of most of it but not all of it.. night videos and pictures will always show the most debris in a pool and sand will show the most, then cartridge filters then DE filters show the least amount of debris..
 

Texas Splash

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I understand that after adding CYA, the need for chlorine changes drastically. Is there a good guide for that in this site?
For that we refer to the FC/CYA Chart. Since you only need about 20 ppm of CYA, your FC can still be on the low side and would be more comfortable to teh skin that 1-3 ppm with no CYA.

You are correct, you would notice sand. Like Casey noted, it's very possible you are simply seeing normal particulates that get past sand, especially at night in front of a light. Could it be algae? ....... dead perhaps which is a lighter off-white or grey color. Your filter pressure doesn't seem like an issue at this time. If the sand was extremely channeled I would expect there could be a lower pressure because the water might flow less impeded through those channels (gaps) back to the pool. A filter with increased pressure would of course be an indication of algae. But if you decide to open it up and do the deep clean you might learn a lot about the pol that way.
 

Newdude

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it's very possible you are simply seeing normal particulates that get past sand, especially at night in front of a light
I’m thinking that with such a (lovely) small pool and so much greenery around it, there will forever be small particles floating around that didn’t make it through the filter yet. It’s similarly proportioned to my larger pool with all the oak trees. I forever had ‘stuff’ floating in there.

It goes back to the turnover myth. Putting the volume of the pool only gets half (?) of the water through the filter due to mixing. The next full volume only gets half of the other half. And so on and so on and by the time it finally all finds the filter, 2 more handfuls made its way into the pool. 🤦‍♂️

*Also, Welcome Issy !!!
 
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lsemprini

Member
Jul 13, 2021
6
Hoi An, Viet Nam
I’m thinking that with such a (lovely) small pool and so much greenery around it, there will forever be small particles floating around that didn’t make it through the filter yet. It’s similarly proportioned to my larger pool with all the oak trees. I forever had ‘stuff’ floating in there.

It goes back to the turnover myth. Putting the volume of the pool only gets half (?) of the water through the filter due to mixing. The next full volume only gets half of the other half. And so on and so on and by the time it finally all finds the filter, 2 more handfuls made its way into the pool. 🤦‍♂️

That's a depressing and very good point, thanks! If none of the other methods work, I could get a few more tarps and totally cover the pool (well, leave the existing 1 foot stripe for sun but otherwise cover the pool. This pool has only a few users, so it can be covered most of the time.
 

lsemprini

Member
Jul 13, 2021
6
Hoi An, Viet Nam
Your filter pressure doesn't seem like an issue at this time. If the sand was extremely channeled I would expect there could be a lower pressure because the water might flow less impeded through those channels (gaps) back to the pool. A filter with increased pressure would of course be an indication of algae. But if you decide to open it up and do the deep clean you might learn a lot about the pol that way.

I just looked at the pressure again and nowadays it's 1 PSI normally and 0.5 PSI just after a backwash. Is that at all reasonable? Everyone else seems to talk about pressures an order of magnitude bigger.

Today, poking around the landlord's pool cabinets, next to their supply of soda ash, I found an unlabeled bag of something that looks like ugly dry fine dirt....dark dirty brown color and so fine that when you squish some between thumb and forefinger, your fingers become painted brown and no grains are visible or feelable. I sincerely HOPE that this is not what the local "professionals" put into the sand filter, cuz it's definitely not sand of any kind.

How fine should real sand filter sand be and should it be brown color? I see there are some pictures of sand in the filter deep-clean pages that you pointed me to, but all those pictures lack scale, so I can't tell how big the grains should really be (like polenta size? like table salt size? like flour size?). Should they be so small that the sand becomes a paste when squished?

Today I tried the few simple hacks (banging on the filter gently with a rubber mallet to try to dislodge/dechannel the sand from outside, running backwash much longer than usual). The first one definitely did nothing. The second one we'll see tomorrow but I don't think it made any difference.

So I may have to get up the courage to undo all the pipes and take the cover off.

Thanks again.
 

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Texas Splash

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Pool sand is typically labeled as #20 silica sand, sometimes called pool filter sand. Should be in the neighborhood of .45-.55 mm in size. It should look grainy and feel gritty. Filter pressures vary based on pump speed. For you to only see about 1 psi means the pump may be on a low speed or the gauge is defective. On high speed I would expect to see a pressure of somewhere between 10-20 psi. The needle should fall to zero when off.
 

Newdude

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dark dirty brown color and so fine that when you squish some between thumb and forefinger, your fingers become painted brown and no grains are visible or feelable
Sure sounds like DE to me which can be added to the sand filter for better cleaning. But I’ve never had either filter so let’s consult @Texas Splash
 

Texas Splash

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You can certainly try some DE if you wish as long as it's not feed grade DE, so be careful about that.

 

lsemprini

Member
Jul 13, 2021
6
Hoi An, Viet Nam
Hard to tell without a pic or two. Sounds like product is labeled much differently over there.

Haha, yes, like no labels. In the whole town (which is a tourist town so has hundreds/thousands of pools) there are only two pool suppliers who operate out of small rickety shops and generally deliver whatever you order in a thin, unmarked plastic bag or (for acid and stuff) an unmarked recycled bottle. Sometimes they can email you a pic of the original industrial-quantity box, sometimes not.

Here's what the mystery powder looks like (hope it's not toxic).

I also put in an inquiry for actual DE and we'll see if they stock it.
 

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RDspaguy

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I thought I would throw it out there that a sand filter, with grains slightly bigger than coarse table salt, is least efficient when clean. There is more space between grains for minute particles to return through. This is what DE does for you, it clogs your filter so it can get smaller particles. Stop backwashing so much, do it once a week or so and see if things improve.
Pressures at the filter depend on many factors, that's why they say to backwash at 10 psi above starting pressure and not at a set number. But seeing no increase in pressure over time is the sure sign of channeling. Deep clean that filter.
 
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