CYA Dropped from 50 to 20??

[alanrmeadows]

Test Results:
FC 6.5
CC 0
TC 6.5
ph 7.5
TA 120
CH 260
CYA 20

I think I've got a problem? One month ago I had a CYA reading of 50. Today I had a CYA reading of 20...both readings were from the the TF-100 test kit. We are probably putting in about 1-2 inches of new water every other day due to what we thought was evaporation. Do you think it's possibly a leak and not evaporation...and that's what caused the dramatic decrease in my CYA level? Could I be replacing that much water thus causing that much of a decrease in my CYA?

Thanks,
Alan
Fiberglass
17,500 Gallons
Sand Filter

 

[257WbyMag]

1 to 2 inches of water every couple of days, along with your CYA loss, would indicate a probable leak.

 

[alanrmeadows]

If I do have a leak but can't get it repaired for a while, what do you suggest I do:
1) Start using tablets so that I know CYA is being added daily in small increments

OR

2) Use stabilizer to get my CYA around 50 and check it every couple of weeks to make sure it is in the 30-50 range

Thanks,
Alan

 

[alanrmeadows]

If anyone could help me with my previous question, I would sure appreciate it. Also, is there anyway for me to detect my potential leak and repair it, or is that a job for the pool guy?

Thanks,
Alan

 

[Terry]

Either way will work. Both require you to monitor your cya. Both have pros/cons. Option one will result in less jugs of bleach to carry and not having to buy cya; however, if you have a lot of sun on the pool you’ll go through more chlorine while at lower cya levels. Option two gets your cya up quicker, but you will need to buy cya and add your chlorine more often. If you do buy pucks look for 99% trichlor. I got a gallon jug of cya reagent from Leslie's for about $20.

You can check for a leak with a bucket test. Turn off any source of water, fill a five gallon bucket with water and set it on the steps. Mark the level of water inside the bucket and the level of water in the pool. Wait 24 hours, stay out of the pool, but let the filter run as normal. Measure how much was lost from the pool, and how much was lost from the bucket. More lost from the pool indicates a leak.

Once you determine you do have a leak you can trouble shoot if it is in the pool shell, suction side plumbing or pressure side plumbing. Run another 24 hour test with plumbing ON. This time you don’t need the bucket. Mark the starting and ending level of the water with a pencil on the shell of the pool, measure and record the difference. Next, run another 24 hour test with the plumbing OFF. Mark starting and ending levels and record the difference. You’ll need to stay out of the pool for these tests too so you don’t alter the results with splash out.

If the pump on loss > pump off loss you can suspect a pressure side plumbing leak
If the pump off loss > pump on loss you can suspect a suction side plumbing leak
If the pump off loss = pump on loss you can suspect a leak in the shell or fittings

 

[alanrmeadows]

I did the tests as suggested and discovered I have a leak. It's actually in two places...there's a leak in the skimmer and water was running down my filter (which I already knew). The pool guy has patched the leak in the skimmer several times for the previous pool owner and is now suggesting that I get a new skimmer. I guess I'm going to bite the bullet and pay around $1,300 for these repairs. I know that sounds like a lot, but there's not a lot of competition in my small community. When my repairs are completed and water is no longer leaking, I would like to get my CYA as high as possible without going overboard. I'm tired of adding so much bleach daily. I know the pool calculator suggest 30-50, but do any of you out there keep it higher?

Thanks,
Alan
17,500 Gallons
IG
Fiberglass
Sand Filter
BBB Method

 

[alanrmeadows]

Is it possible to lose FC due to a leak? Or does FC remain in the water that has not leaked out of the pool? I'm still losing around 2 ppm overnight and am wondering if the leak has anything to do with it?

Thanks,
Alan

 

[svenpup]

The same way that CYA goes down when high CYA pool water leaks out and is replaced with low (no) CYA tap water, FC goes down when high FC pool water leaks out and is replaced with low FC tap water.

If you aren't adding water overnight (e.g. via autofill) than the 2ppm indicates the presence of organics and the need to shock.

 

[alanrmeadows]

After fixing my leak, I decided to retest my CYA level. Using the test included with the TF-100, I was still able to clearly see the black dot at the 20 level. At that point I ran out of solution. Should I assume that my level is either 10 or 0? If that is the case, is it possible to lose 5-7ppm of chlorine per day if that low of a CYA level is accompanied by daily additions of water due to the leak in my skimmer? I'm just wondering because it seems like I was using a jug of bleach a day.

Thanks,
Alan
IG
Fiberglass
17,500 Gallons
Sand Filter

 

[Bama Rambler]

It's possible to lose more than that per day with no CYA in the water. The sun will burn up FC very quickly with no stabilizer. You could use tablets to get it back up if you wanted to. Or just add some back in if the leak is fixed.

If you use tablets it's going to be slow process that you might not want to wait on.

 

[Butterfly]

........I'm just wondering because it seems like I was using a jug of bleach a day.

What size jug? A 96oz jug would increase your FC by about 2.5 which seems like normal loss.

I suggest you add enough CYA to get to about 30, wait a week, and then retest. You will be somewhere between 30 and 50. The test accuracy is +/- 10.