Frustrated!

[Westy]

We purchased home in August with 15,000 gal. Hawaiian lap pool. CYA levels were through roof at 300 ppm. No FC using Taylor drop test. After shocking, FC would drop to zero in a few hours. I've drained/refilled pool 3 times by draining about half the water each time. CYA tests during drain/refill cycle was done using test strips. The test strips showed a CYA drop to about 30-40. Yesterday I purchased replacement CYA reagent for Taylor test kit that previous owner left me. Test showed CYA still over 100! Could something be giving false positive on drop test for CYA? CYA level should not still be this high after drain/refill cycle. I still can't keep FC. I can bring FC to 15-20 ppm with the addition of bleach (no stabilized Cl being used), but it drops to zero overnight. I've added bleach 3-4 times, but it drops in hours and TC stays high. Any ideas would be appreciated.

I corrected numbers in original post. I've shocked with bleach to 15-20 ppm, and then had FC drop to zero.

[chem geek]

Did you do your drain and refill in two steps -- drain half, then refill? Or did you do it with a continuous drain in one part of the pool will filling in another part and just keeping track of how much water? If I assume the former, then your CYA would go from 300 to 150 to 75 to 38 and that is consistent with your test strip reading.

I am not aware of what would cause interference in the Taylor CYA test which just adds melamine (which combines with CYA to form melamine cyanurate which is minimally soluable and therefore produces a cloudy precipitate). If the pool water is not near room temperature, then you can get a false reading, but it will be too low because either the water is too cold so that the precipitate takes too long to form or it will be too hot so that the precipitate is more soluble.

Nevertheless, I would say that having your chlorine used up so quickly overnight means that there is something in your pool consuming lots of chlorine. It could be nascent algae or lots of organics or ammonia/urea. You should continue to shock with bleach and try and keep the FC level up by adding chlorine several times if you can (at least twice per day -- morning and night). Eventually, you will breakdown or kill whatever it is that is consuming the chlorine and the chlorine should hold its level overnight (not during the day, however, if it's exposed to sunlight -- even with CYA it can get cut down by half in a full day of strong sun). You might also check and clean your filter if it looks like its trapped a bunch of junk (dead algae, organics, etc.) as the chlorine will also get used up trying to breakdown whatever is stuck in the filter, not just what is in your pool water.

After your chlorine holds, try retesting your CYA level with your Taylor test kit. Let us know the results. If the measurement is now around 30-40 ppm, then whatever it was you killed or oxidized with the chlorine must have interfered with the Taylor CYA test. That would be good to know about.

[waterbear]

We purchased home in August with 15,000 gal. Hawaiian lap pool. CYA levels were through roof at 300 ppm. No FC using Taylor drop test. After shocking, FC would drop to zero in a few hours

Which Taylor kit are you using. If the FC test is a DPD test (K-2005 kit and others), this can bleach out when chlorine levels are high, giving a false low reading. If you are using the FAS-DPD test (K-2006 kit) then I would trust your FC results. You can always test the TC with an OTO test (yellow reagent found in those cheapie 2 way testers). It will give you a good idea if there is chlorine or not. If it is clear there is NO chlorine, if it is yellow there are normal chlorine levels. If it is deep yellow to orange, you have shock levels of chlorine, if it is reddish to brown you have a poolful of bleach!

I've drained/refilled pool 3 times by draining about half the water each time. CYA tests during drain/refill cycle was done using test strips. The test strips showed a CYA drop to about 30-40.( I wouldn't trust this reading!) Yesterday I purchased replacement CYA reagent for Taylor test kit that previous owner left me. Test showed CYA still over 100! Could something be giving false positive on drop test for CYA?

I would trust the melamine precipitation test in the Taylor kit over the test strips! It is really foolproof. If there is CYA present then you will get a while precicpitate in the water, period! A couple of thoughts as to why you are still testing high:

1. CYA can deposit in the pipes and even on the plaster of the pool and will continue to dissolve over time as you drain and refill so you might have to do it more than you think you do.

2. Your CYA levels were much higher than you thought when you started. There is really no easy, precise way to determine CYA levels over 100 ppm for the home user.

3. The dropper bottle or test vial in you kit might have a CYA residue that is giving you a false high reading. Try cleaning them out or even purchasing new ones from Taylor.

I am putting my mony on 1 and 2 above!

CYA level should not still be this high after drain/refill cycle.

It is entirely possilbe it is if there was CYA depsosited in your plumbing and pool surface that is now redissolving. This is actually fairly commen.

I still can't keep FC. I can bring FC to 15-20 ppm with the addition of bleach (no stabilized Cl being used), but it drops to zero overnight.

AHA!, if you are adding chlorine and it is testing correctly and then overnight it is zero then you have algae! (or some other nasty growing). This creates a chlorine demand. If your CYA level is really around 100 then you need to be bringing your FC to about 25 ppm to do any good and you need to keep it there by adding enougn chlorine 2-3 times a day to maintain that level. You should find that within a week your FC WILL hold overnight. High CYA levels require running higher FC levels for both normal chlorination and for shocking.

I've added bleach 3-4 times, but it drops in hours and TC stays high. Any ideas would be appreciated.

Low FC and HIgh TC--this pretty much confirms what I just said above. Raise your FC levels to about 25 ppm and KEEP THEM THERE by adding bleach 2-3 times a day until your FC holds overnight. You might even need to go up to 30 ppm. It is pretty obvious from this that your Taylor kit is right on the CYA readings. Ditch the strips! Dilute a sample of the water with distilled water 1 to 1 and test that for CYA. Multply the results by 2. IF you are still off the scale then your CYA was MUCH higher than you thought when you started!. Test strips do not have a lot of precision (different from accuracy, they ARE accurate). and the melamine precipitation test for CYA will not test levels above 100 ppm without dilution.

I corrected numbers in original post. I've shocked with bleach to 15-20 ppm, and then had FC drop to zero.

Hope this is helpful.

[chem geek]

waterbear's advice is, of course, right on the money. The thing is, that if the CYA level is really still over 100 (which could be true if you started with 800 then with dilution this would be 400, 200, 100), then the amount of Free Chlorine you would need to kill algae would be really, really high at about 40 ppm FC. At 30-40 ppm CYA, killing algae needs 15-20 ppm FC. Why don't you try waterbear's advice of maintaining 25 ppm FC and see what happens and let us know.

After this is all over and you've gotten things under control, you should not use any chlorine sources that contain CYA, such as Trichlor tablets or Dichlor powder. Just use chlorinating liquid or unscented bleach as your sole source of chlorine (at least until next season when you might need to add more CYA by using Trichlor for a while or adding CYA directly).

[Westy]

I appreciate the replies. Let me respond to some of the points and questions for clarification.

1. The drain/refill cycle was NOT done with simultaneous addition of replacement water, thus my current level

of CYA of 100+ was certainly much higher than the 300 ppm as indicated by the test strips.

2. While I've been attempting to get CYA levels in order (nearly 3 months or so) the FC level in the pool has

been hovering near zero. So as to not dump $$$$ into the pool, I was not adding much Cl. Maybe the Cl

demand now is necessary to oxidize what had built up. Oddly, the pool looks great with very clear water.

Chem geek, I might focus on getting FC level up before attempting to tackle the CYA, then retest CYA after Cl levels are OK. If CYA tests under 100 at that point, that would be an interesting finding.

waterbear, the test kit is Taylor K-2005. I'll try an OTO test and see what I get. I think you are right regarding residual CYA in plumbing, filter, etc. I have cleaned the filter (cartridge) several times, but if CYA is pervasive, maybe I'm still picking it up from surfaces, etc.

I'll try another CYA test with 1:1 dilution to confirm value, then try to get FC up to required level and maintain it.

Again, thanks for the advice and input.

[Westy]

I think I've just about got things straightened out, so I thought I would write an update. I've done a few more partial drain/refills and I've got CYA down to 60. While doing the drain/refill cycle, I've added a minimum amount of bleach to basically keep visible algae away, and the pool looks great. I shocked to about 30 ppm two days ago. This morning, still had FC reading above 5 on DPD test and tested over 5 with OTO test. TC also read over 5. Within the last half-hour, I had a FC of 3 and a TC between 4 and 5. I cleaned the cartridge filter between the morning and afternoon tests. I just added more bleach and will continue to do so until residual FC is maintained. What do you guys think, am I close to having this balanced?

[waterbear]

If you are going to maintain your CYA at 60 ppm then keep your FC at 5-10 ppm for normal chlorination and shock to at least 20 ppm ppm when you need to kill algae or burn off combined chlorine. This should give you enough active free chlorine in the water for the amount of stabilzier present. If you want to run at more normal levels of 3-6 ppm and shocking to 15 ppm then get the CYA below 50 ppm.

[Westy]

If you are going to maintain your CYA at 60 ppm then keep your FC at 5-10 ppm for normal chlorination and shock to at least 20 ppm ppm when you need to kill algae or burn off combined chlorine. This should give you enough active free chlorine in the water for the amount of stabilzier present. If you want to run at more normal levels of 3-6 ppm and shocking to 15 ppm then get the CYA below 50 ppm.

I may go ahead and get CYA down under 50 to be able to run lower levels of FC, It has just been such a chore to get this thing down under 100. I must have started with CYA levels that were pushing 1000 ppm based on the water change I've done! Either the previous owner of the house never checked the CYA or he knew they were moving out of here and he did not want to bother. I just checked and had FC = .5 and TC = 1, so I've still got Cl demand in the system. Looks like I'm still a bit away from maintenance levels of FC at 5-10 without adding Cl almost constantly.

[Westy]

If you are going to maintain your CYA at 60 ppm then keep your FC at 5-10 ppm for normal chlorination and shock to at least 20 ppm ppm when you need to kill algae or burn off combined chlorine. This should give you enough active free chlorine in the water for the amount of stabilzier present. If you want to run at more normal levels of 3-6 ppm and shocking to 15 ppm then get the CYA below 50 ppm.

I went ahead and did another partial drain and have CYA levels in the 40's. My FC is holding nicely now also with minimal addition of chlorine. Things are looking good! I am still amazed at the levels of CYA that I had after we purchased the home, obviously some folks have an approach to pool maintenance where ignorance is bliss.

[Mo-mo]

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