Question/opinions on filtration and media

PanamEric

Active member
Hello,

I am new to this forum and find it very informative. I am wondering about filtering media but am not sure where to post my questions. I have a few of them...
First I have had a pool in Canada for the last 10 years which is running on SWG with Zeolite in the sand filter and am very happy with the setup.
I now work in Panama (Central America) and have a 25,000gls plaster pool with a 600lbs sand filter. (isn't that oversized?)
Given the hot weather and heavy rains and outrageous chlorine prices (3 times the price from back home) I have switched this one to SWG as well.
I know I have to change the sand in my filter.
I was told by an online pool store support guy to put 200lbs pea gravel at the bottom and 400lbs sand on top...but I don't understand the logic?? Isn't the flow from top to bottom? And if so would it not be more efficient for the water to go through the coarse medium (pea gravel) first and then the finer medium (sand) last? If that's the case, then shouldn't the sand be at the bottom and pea gravel on top?

I am tempted to go with zeolite but the prices here are very high...required amount of zeolite(300lbs) is same price as a new filter and pump back home (nearly $500).
So I am wondering if I would still get the benefits of zeolite if I were to use part sand and part zeolite in a scheme similar to sand and pea gravel. I was thinking 400lbs sand and 100lbs zeolite? I am thinking it should improve the filtering but could be mistaken.
And if I do that should I put the zeolite first, at the bottom or at the top?
And last question: while searching for the above I stumbled across perlite as a filter medium. It seems to be used only as a fine powder in DE filters in lieu of the DE. Would it work using coarser perlite in lieu of sand in a sand filter? Has anyone tried that?
Thanks in advance for any input...
Eric
 

Melt In The Sun

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PanamEric, welcome to TFP!
First of all, I'm not sure you need to change your sand. Actually, I'm pretty sure you don't need to. What's your reasoning for doing so?

Now that you mention it, I'm not entirely sure why people use pea gravel in the bottom of sand filters :scratch: I think it is intended to keep sand grains from getting into the laterals, but I know it's not necessary; some people do it, some don't bother and aren't any worse off.

I don't think perlite would work in a sand filter. I imagine it would probably break apart into dusty particles and get blown back into the pool through the laterals, or all carried out by backwash.
 

duraleigh

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Welcome to the forum :lol:

Like MITS, I don't believe you should automatically change the sand unless you have a very specific cause. Also, you can't get a filter that's too big.........only too small.

My Triton sand filter called for "optional" pea gravel on the bottom and I chose not to use it. I have never seen any adverse effects from it's absence.
 

dmanb2b

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Welcome to TFP...you've gotten great advice so far. Some folks never change their sand :goodjob:
 

teapot

In The Industry
Jul 25, 2009
574
London and France
If you are using SWG then there is almost no point of switching to zeolite IMO as the ion exchange feature doesn't work in SW pools. There isn't really a need to change the sand either providing it doesn't get calcified from hard water. That said sand does need looking after and cleaning as it does get sticky with biofilm and body oils, sun cream etc so does require cleaning. It does not get its sharp points worn away as many sellers state.
 

PanamEric

Active member
Hello All...
and thanks for the answers.

My understanding of filtration is a two part process: mechanical filtration and chemical balance. I normally manage to keep the chemistry within range but do have to add salt and stabilizer frequently (because of heavy rains) and calcium occasionally.
I can't seem to manage to get my water cristal clear like I get it in my other pool in Canada. Of course the temperature is much warmer here (never below 84f). The water temp is usually around 86 (80min recorded to 94max recorded).
Test results today (had heavy rains last night)
CH 230
TA 50 (yesterday 60)
PH 7.4 (yesterday 7.6)
FC 1.5 (yesterday 2.5)
Cyanide 40
Temp 83f
The water is not green but fairly cloudy. The shallow end is visible but not clearly, deep end not at all.

My reasoning for changing the sand is :
1-The original owner of the house does not remember changing the sand since installing the pool 18years ago. I don't even know if there is 600lbs in there and if it is the right sand.
2-I have good flow (1.5hp/100-120gpm) but yet the filter can't seem to keep the water clear. Its cloudy and we can't see the drain in the deep part.
3-When I try to vacuum the dirt comes out the return. The only way I can achieve some vacuuming is by topping off with DE and even then the dirt comes through after a few minutes.
4-Finally I have to change a cracked bulkhead on the filter (Triton-100 side mount) and I have never done it before but I am pretty sure I can't do that without emptying the sand.
So since I assumedly have to take out the sand I figured it could not hurt to put fresh sand. Would 1/3 zeolite 2/3 sand(by volume) work? and if so which should I put at the bottom?

Thank you for the input . This forum rocks.
Eric
 

PanamEric

Active member
teapot said:
If you are using SWG then there is almost no point of switching to zeolite IMO as the ion exchange feature doesn't work in SW pools. There isn't really a need to change the sand either providing it doesn't get calcified from hard water. That said sand does need looking after and cleaning as it does get sticky with biofilm and body oils, sun cream etc so does require cleaning. It does not get its sharp points worn away as many sellers state.
Thank you for the input Teapot!
Agreed the ion exchange does not work...what I am after is improved mechanical filtration and reducing backwash frequency.
Wouldn't zeolite do that?
Thanks
Eric
 

teapot

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Jul 25, 2009
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PanamEric said:
Cyanide 40
2-I have good flow (1.5hp/100-120gpm) but yet the filter can't seem to keep the water clear. Its cloudy and we can't see the drain in the deep part.
Eric
2 problems:
If you really have CYANIDE in your pool the water will never be clear as all the dead bodies will make it cloudy :lol: Cyanuric acid however is ok :wink:
A good flow 100-120gpm through a filter is not going to give you clear water. To filter you only want 30gpm/sq ft, (check your filter spec) or you are jet washing the sand nice and clean but pushing all the dirt into the pool. Another alternative is the sand is channelled so allowing easy paths for dirt to pass through.

The fine sand at the top of the filter is to produce a filter cake in the first few inches so that all the dirt is trapped at that level and can be backwashed away easily. If the dirt works it's way deeper through the filter then it becomes much harder to clean via backwash and can then become a source of bacterial/viral growth with a constant supply of food and the sand becomes colonised and coated in biofilm which chlorine alone cannot breakdown. This biofilm causes the sand to stick together and "pebble" producing channels between the pebbling that water can easily pass through.
 

PanamEric

Active member
Hello Teapot,

My filter TR100 is listed as having 4.91sq ft and Pentair lists 98gpm as optimal flow rate (@20gpm/sf). At 30 it would to 150gpm(147.3 to be precise).
So it would appear that my flow is between Pentair's and your recommendation.
Also I don't have a flowmeter but timed how long to fill a 5gls pail, hence the range as I got varying times.
So how do I get this water clear?
Thanks
Eric
 

teapot

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Jul 25, 2009
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Time to look inside the filter then as sand as bad as it is should still produce clear water. I don't like DE that much so use floc occasionally but by the sound of it you need to inspect the sand first.
 

waste

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Eric, welcome to TFP!!

If vacuumed dirt is returning into the pool you either have channeled sand (as per Teapot) or a multiport gasket/ o - ring issue.

Which bulkhead fitting needs to be replaced? If it's the top one, you might be able to change it with the sand still in the filter :cool: . As a rule of thumb, I always went with "what you do to one [bulkhead fitting], you do to both" as they should wear evenly and, if the bulkheads end up slightly out of line, the multiport wont seat correctly.

If you end up changing the sand, I'm a proponent of replacing the first 1/4 sand with pea gravel (in your case it'd be 150 lbs). You get improved flow around and through the laterals, less chance of bionasties colonizing in the bottom of the tank, sand won't clog the laterals, and, if a lateral breaks, you won't end up with sand in the pool. (there were a couple threads a few years ago on this topic - if you'd like I will find them and link them here for you :) )

(I also saw your CH issue and am as puzzled as Richard :? )
 

duraleigh

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I think this thread is going down the wrong path. NO filter on earth can keep a pool clear if the chlorine is not held high enough and the test results indicate that is the case.

I would suggest you shock the pool correctly according to Pool School until the water clears. You may likely find you have no filter issue but a chlorine issue.
 

PanamEric

Active member
Thank you all for the answers...
I wish I would have found this forum 10 years ago!

First: Teapot: Report on sand inspection
1-I spent the most of afternoon trying to clear out channeling as per the instructions on the post I found here.
Pretty much the bugs that stopped me because the water was still not clear after a little over 3hrs, but I was nevertheless amazed at the amount of dirt that came out of there.
2-Measured the freeboard on Triton II-100 which is supposed to be 11-1/4" (top of bulk head) but I have a little over 14".
According to my calculation I am missing 1.5 cu ft of sand or app 150lbs if my calculations (30"dia x 3.75"high) are right. I used 100lbs per cu ft.
3-I closed everything up -without adding any sand- and ran a backwash and rinse.
4-Tried vacuuming and dirt starts coming out the return after about 90 seconds.
5-Stopped vacuuming and Added 1-1/4 cup of DE which is what I need to increase working press by 1lbs.
6-Added 6lbs calhypo (starting to feel like when I am filling up the car in Canada) and will hopefully wake up to a clear(er) pool in the morning. Thank you Duraleigh
Waste: It is unfortunately the bottom bulkhead that I need to remove...and I should have been more precise. Its not the bulkhead that needs replacing but rather the external spacer but I have 2 complete ones and will likely end up changing both unless visual inspection reveals it is really not warranted on top one.
Yes I would like to read the thread on the topic of pea gravel, if not too much trouble.

and finally the CH issue...it turns out (thanks to a phone interruption) that if I wait 5 minutes or so the reagent turns (about) the right color and renders believable results. I don't understand it but the CH level appears right. Still interested -out of curiosity- if someone has a chemical explanation for the delayed reaction.
Thank you all. Really appreciate the effort.
Eric
 

duraleigh

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6-Added 6lbs calhypo (starting to feel like when I am filling up the car in Canada) and will hopefully wake up to a clear(er) pool in the morning.
Good morning, Eric,

I think that's a good start but you are not shocking according to Pool School if this is all you do. Please read the article.....you will find it is a process that can take several days not just a one-time dose.
 

4JawChuck

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Jun 13, 2010
223
Winnipeg, Manitoba, Canada
It took a week of constant shock to clear my pool when I first took ownership of the house, you need to stay on top of it to sanitize the entire pool including the accessories (leaf skimmers, toys, robot or Krawler etc.). More than a few backflushes were required during that time to clean the sand filter or accumulated dead algae before I got it all out. Since my CYA was high I had to keep the PH below 7.8 so the chlorine would work which meant I had to seesaw the PH back to proper levels as the FC levels dropped.

A one time dose is usually never enough, think of it as a process that needs to be maintained long enough to kill everything living in the pool...some algae are very resistant to chlorine and form a resistant biofilm that requires brushing to break.

I agree you don't have a filter issue but likely a biological one.
 

teapot

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Jul 25, 2009
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London and France
duraleigh said:
I think this thread is going down the wrong path. NO filter on earth can keep a pool clear if the chlorine is not held high enough and the test results indicate that is the case.

I would suggest you shock the pool correctly according to Pool School until the water clears. You may likely find you have no filter issue but a chlorine issue.
I think you'll find PanamEric commenced this thread discussing filtration.......

On a positive note doing both will produce the best results as chlorine is still consumed by dirt in the filter and PanamEric said he had plenty of that too.

Now I'll put my tin hat on and await the PM :wink:
 

PanamEric

Active member
Thank you for these posts Waste.
After reading all I kind of made up my mind...and I believe I will pea.
You will guess that this means that I will change the sand. Despite very valid arguments against the need to change the sand in my filter I have decided for it. No dis intended to anyone!

My reasoning was explained earlier in this thread but I have a few additional reasons that kind of convinced me.
The fact that this old sand is so LOADED with organics that 3 hours of pressure washer on the sand did not see clear water. If anything the water seemed to be getting dirtier as I went deeper with the nozzle.
Other reasons: calhypo here is a whooping $3/lbs. In the last 4 days I have spent over $100 (over 35lbs-6 shocks) in calhypo and I am freaking out thinking of the amount of organics left in that sand. I see no end to it and will probably spend 2 times or more the cost of new sand trying to clean the old one. I am thinking that with new sand I will only have the organics in the pool left to burn off and I should be able to get this done more easily and quickly.
Also everything in this filter is 18y/o except for the parts I changed since I got here. Sand was never changed so I suspect if the laterals are not broken they are surely very brittle and I have a complete new set on hand. It would be kind of dum not to replace them while I am down there, at least I think.
Still debating if 100lbs of zeolite would make sense to improve mechanical filtration...
Does anyone know if the Triton TR100 allows you to drain the sand through the drain plug or not?
Thank you all for your precious input. I hope to post a nice picture with cristal water soon.
Eric
 
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