Can't get CYA down...

[Bpropheter]

Last week I took my water into the pool store for a free test. The CYA was at 201 and I was out of chlorine. After asking what I should do, the pool store directed me toward cal-hypo to avoid adding more CYA to the pool. That didn't make sense to me since calcium was also high. They said there wasn't much we could do as a full drain was really what was needed.

We just re-did our pebble last year so it didn't make sense to me that I was needed to drain my pool again already... Anyway, long story short is I did lots of internet searching and landed here. Read a ton and ordered the TF-100 XL kit.

My pool is clear, though I've struggled with the beginnings of algae showing for the last 10 or so months, especially when the weather gets into triple digits. So about 1x a week, I'd shock and brush and it'd stay clear for another week or so.

Over the weekend, while waiting for my test kit, I decided to try the differential drain technique. According to my math and the run time of the pump, I should have removed about 2/3 of the water from my pool in the time I ran the submersible pump. I then turned the pool filtration system back on, poured in a gallon of 10% chlorine (just so something was in there) and ran the system overnight. The test kit got here today and I tested my water. The CYA doesn't register on the test... I even did the dilution method and multiplying by 2 as described here, and it still is just below the 100 line... so my CYA is showing as 200+ with the TF-100 after draining 2/3 of my pool??

So my question is, is it more likely that my water was way more than the 201 that the pool store registered last week, that my drain technique didn't work right, that I'm doing the test wrong (I did it a dozen times...) or something else?

Full test results:
FC 1
CC .5
PH 7.5
TA 220
CH 500
CY 200+

With temps over 100 during the day, I don't dare completely drain the pool. Advice extremely welcome. Thanks!

 

[Texas Splash]

Welcome to TFP! Your scenario proves two things we always state here at TFP: First, pool store testing is almost always skewed. Two, their advice isn't much better. Anyone in AZ who would recommend using cal-hypo needs to read our ABCs of Pool Water Chemistry. Now that you are using a TF-100, my guess is that the CYA was much higher than you (or the pool store) believed. Your own TF-100 testing doesn't lie, so more water exchange is necessary. The best way is just to drain it quickly and refill, but many in your area wait until winter so the sun isn't so hot on the exposed plaster/pebble. But if you continue to do the drain exchange, keep going until the CYA is down to at least 70-80.l That way you have a decent chance of performing a SLAM Process to remove the algae and continue with the rest of the season. Good job getting the right test kit. You're in charge now.

 

[mgtfp]

Trust your own CYA test, the pool shop test is likely wrong.

How have you been adding chlorine in the past, did you use Trichlor? With each ppm of chlorine you add with Trichlor, you also add 0.6ppm of CYA. So, as an example, if you added 2ppm of chlorine each day for a year with Trichlor, then you'd have also added 438ppm of CYA.

 

[Bpropheter]

Yes, that was my conclusion, as well. I was using Tichlor pucks and dichlor for shock every week...

So my options seem to be:

1. Try to ride it out as is until temps drop
For this route, is it realistic that I can keep the pool in swimmable condition until then?
What is a "safe" temperature for draining a pebble pool? Temps can be above 90 well into Sept here

2. Try to do another water exchange
With 200 CYA, I'd have to exchange nearly all the water. How realistic is that with this method? Seems like water would start mixing before that'd happen.

 

[mgtfp]

I think, riding it out will be difficult. To keep your pool sanitized and free of algae, you need to adjust your FC level to your CYA level according to the Chlorine/CYA-Chart:

The Free Chlorine and Cyanuric Acid Relationship

Managing your cyanuric acid and Free Chlorine levels is key to stabilizing your pool. Learn how these two items affect each other.

www.troublefreepool.com

E.g. at CYA=50, you need FC around 7. At your CYA level, you are way off chart. I guess that at CYA=200 you needed about 25ppm of FC, and at CYA=400 probably nearly 50ppm of FC. And should you need to SLAM to fight an algae bloom (which is very likely to happen at these CYA levels), then you'll need an FC in the hundreds. That is just not manageable, and you just don't know where you are, is it 200 or 300 or 400? If the reading after the 50:50 dilution was just below the 100 line, then it'll probably be somewhere between 200-300.

I would start with another CYA test with higher diluted water until you get a reading below 100, which you then have to scale up according to your dilution to get the actual CYA reading of your pool water. Then at least you'll know if a partial drain will cut the mustard, or if you are facing more or less a full replacement (just leaving a bit, because you'll want some CYA afterwards anyway). But I fear that a water exchange is your only option.

EDIT: To minimize mixing of the fresh water with the old water, you would try to pump from the bottom of the pool and refill at the top.

 

[mgtfp]

But I can't help you with the temperature part of your question, no experience there. Hope that someone else will chime in there.

 

[Bpropheter]

Yea I've seen the chart... I'd love nothing more to do a complete drain and just start over. The problem is that the temps here are 100+ for the foreseeable future. From what I've read, I shouldn't do a drain until temps are at least below 90 (some say 85). So are you saying I should do the differential drain technique again? Just worried about wasting so much water potentially doing several exchanges that equate to more than the total water in my pool...

 

[mgtfp]

It will probably be difficult avoiding mixing of the water if you can't ensure that your fill water is warmer than the pool water. But I guess it would still take same time to mix, if you stopped the circulation, pumped from the bottom and refilled through the skimmer.

In @JoyfulNoise 's partial draining, he didn't just rely on the temperature difference between old and fill water, he also had 3400ppm of salt in the pool due to running a SWG, which increases the water density to start with. JoyfulNoise did his water exchange as efficiently as possible, but he had time to get that all sorted. I am not sure sure if you have that luxury. And I hope that you wouldn't need more than your actual pool volume. To get down from let's say 250 (just a guess...) to 50, you'd probably have to replace 80% of your water. Even if the water starts mixing too quickly and you'd actually replace only 60% of the water, you'd be at CYA=100 - not ideal, but probably manageable for a while

Maybe you could actually add let's say about 100kg of salt to your pool first to increase the density - not sure what other's think of that. That would bring salt up to about 2700ppm, and down again after the partial drain. Do you know what your your salt is currently?

If you decided to postpone draining until it get's colder, there might a chance to keep algae in check by using Polyquat60 - this is the only algaecide tolerated here, don't use anything else. But that won't be cheap either. Certainly stay away from any copper based algaecides, you don't want to stain your brand new pool surface.

From a sanitation point of view, you'd probably be OK if you kept FC above 10ppm. But again, we would need to know the exact CYA level to calculate a safe FC level to keep at least bacteria in check. And keeping FC that high will make it impossible to monitor your pH, you could wreck your pebble surface by adding too much acid thinking you have high pH.

Don't know how much water costs in your area. But maintaining the required FC level with CYA>200 sounds very difficult to me and doesn't sound cheap to me either, neither will be a weekly dose of Polyquat60. And once you have to SLAM, you're stuffed. You mentioned that you were already struggling with algae. And Polyquat60 is good at preventing algae from growing, but as far as I know not as good in killing already existing algae. And finally, not being able to measure pH due to high chlorine for a long period of time, is also a big problem in my opinion.

 

[mknauss]

Draining - Further Reading

www.troublefreepool.com

 

[mgtfp]

Draining - Further Reading

www.troublefreepool.com

That sums it up, didn't know there was a school article on draining. If you can manage to keep your fill water 20F colder than the pool water and there is no salt in the water, then you just reverse it: Pump from the top and fill at the bottom.

 

[mknauss]

In Arizona right now, I suspect the fill water is warmer than the pool water.

CH will be elevated. So I would plan to pump from the deep end and add at the surface. Go about 10% over on the exchange. Always has worked for me.

 

[Bpropheter]

Ya I read that article and that's exactly what I did this weekend. By my math, I exchanged 7000 gallons and still have a CYA of 200.

So if my CYA is 200 and I want to try to get to 30, that means I need 85% new water. (Is that math right?)

Should I overshoot and try for 100% assuming there will be plenty of mixing?

And yes tap water is about 85 and pool is about 86.

 

[mknauss]

Correct. Run through 100% of your pool volume.

The process is far better with high salt levels in the pool water and/or large water temperature variances. But you are dealt the hand you have.

 

[Bpropheter]

Alright I did a water exchange over 2 days. By my math, we should have drained 120% of my pool volume. Was hoping for a cya of around 30. Test showed 50 (between 40 and 50 and rounding up). Not as low as I'd hoped but should be manageable right? Without chlorine added or pump running that long, my pool got quite green.

So cleanedmy filter and started a SLAM this morning (bringing pH down to 7.2 and fc up to 20).

I brushed the pool and it already looks way better. 1 question now: I have a suction vac and the hoses are ribbed. I can see green in the hose. Do I need to somehow clean out all this hose? Or will the slam process take care of it?

 

[mknauss]

You want to get to that algae. If it is stuck in it, you need to scrub the inside some how. Also pump the SLAM level FC through the hose(s) as much as possible.

 

[Bpropheter]

How long does a SLAM typically last? My pool was starting to green but nothing solid in the water.

On day 4 and the pool has never looked more clear. It's been like this since yesterday but overnight FC still dropping. Anything else I should do/be checking? Testing and adding chlorine several times a day but keeping FC at 20 in the AZ sun is a difficult task

 

[mknauss]

Check any hiding places. Light niche, skimmer throat, weir doors.

Stay at it. You are close.

 

[Bpropheter]

Finished slamming yesterday!! My tests look good except that Total Alkilinity is high (even after wiping after each drop). I tried lowering by lowering pH and aerating but it barely moved. At this rate I'd need quite a bit of acid to lower TA. There seems to be contradicting information. Should I lower TA? Or am I fine as long as I keep an eye on pH?

Test results

FC 9
CC 0
pH 7.8
CH 300
TA 130
CYA 50

 

[mknauss]

Great job on completing the SLAM process.

Your fill water keeps upward pressure on your TA. You will get waterline scale more quickly if you do not lower the TA. So it is up to you.

If you wish to lower TA, when pH reaches 7.5, lower to 7.2. May be every day or every other day.

 

[Bpropheter]

Awesome that makes sense. Already have scale so would like to avoid more.

Have one more question about the CH test. The test seemed to be going purple instead of blue so I added the 5 drops of regent first. Now the test looks like the water goes blue but there are suspended particles in the water thar are purple... But I can definitely see when the water changes. Is the test accurate still?

I haven't tried adding distilled water yet as I don't have any around.