Low Cya and it won't go up

[vanman2501]

My pool is about 10 years old now and the problem I am having this year is that I can't get my CYA show a reading.
My readings
FC 0
PH 7.5 today after rain 7.2
TA 120
CYA 0
When I shock the pool I will get a FC reading between two and four. It will hold for about 4 hours then return to 0
I have added about three times the amount of CYA as the pool needs and still on reading.
I tried a new testing kit. I tried a test strip kit. I tested my neighbors pools and all their readings are good and all the kits had the same readings so my test kits work.
I thought I had a bought bad CYA so I bought more and still no reading.
I have no idea what to try next.

vanman2501

[chem geek]

Do you have a Taylor K-2006 test kit or is your CYA test at least one where you mix half pool water with half reagent and add it to a tube until a black dot no longer is visible (see this link, for example)? If not, then your test kit may be bad -- test strips in particular are notorious for mis-reading CYA. Even if it read something in other people's pools, there may be something in your pool interfering with an inferior test. The turbidity test works reliably.

You can also take a small amount of CYA and add it to a bucket of tap water to see if your reagent is good and measuring properly. 1/8th of a teaspoon of pure CYA in 2 gallons of water is around 75 ppm. Note that CYA will not register immediately as it takes some time to dissolve.

How did you add your CYA to the pool? If you added it to the skimmer to get caught in the filter, note that it can take up to a week before it all dissolves, though usually it's a few days. It is not immediate.

As for your chlorine loss, though it will drop quickly during the day if there is no CYA, dropping roughly in half every hour, you should also check the overnight (no sunlight) loss just to make sure you don't also have nascent algae growth in which case you should shock your pool by raising the FC to a higher level, probably around 10 ppm.

[vanman2501]

I have two different test kit both use the black dot, one is from the start of this year the I purchased a week ago I also purchased a test strip kit. I added the stabilizer the same as I always do, I put the pump on recirculate and dump it in the shimmer. I leave it on recirculate for 24 hours before putting back on filter. Even though I have been slowly adding stabilizer since May, plus I use trichlor pucks so I should be getting CYA from them also. I don't have any algae in the pool even though my chlorine reading is 0. I have been adding bleach to try and keep the chlorine level up enough to keep the algae from forming. I tried shocking the pool heavily for a week but that didn't help. I thought just maybe I had to much CYA in the pool so I took some of the water and started diluting it but nothing changed.

vanman2501

[chem geek]

If your chlorine level is at 0, then bacteria can be consuming the CYA and creating a high chlorine demand as well. If that is the case, then you need to add lots of chlorine to stop this process (i.e. kill off the bacteria) and it could take a lot of chlorine to do. When you first started this, the chlorine would read briefly for some hours, so that was good, but having it drop to zero is not. Just keep adding chlorinating liquid to the pool until the FC starts to hold. I wrote a timeline own experience with this problem in this post.

[madwil]

did you backwash after adding the CYA? if so, you could have washed it out of filter and it never got to pool...

[Watermom]

it wasn't in the filter. He had the filter on recirculate.

You don't want to put it on recirculate and then put the cya in the skimmer. Recirculate means you bypass the filter so the cya would just be blown through into the pool and lay on the floor of the pool.