Trouble Keeping Chlorine Levels Up

I am using a combination of bleach (8.25% from WalMart) and 3" pucks from Costco in a Frog feeder. I have an approximately 20,000 gallon IG vinyl pool. Using the Taylor test kit, my pH is consistently around 7.0 to 7.2 (seems like I've poured a lot of Borax into the skimmer this summer) and my Alk is consistent at 90 ppm. I know my CYA is probably off the charts because I have been using the 3" pucks for years (I tested recently and it measured around 100 ppm). However, water is clear and beautiful.

My issue is maintaining chlorine levels. If I pour an entire jug of the bleach in on one day (keeping the 3" pucks in the feeder), my FC levels are very low the next day. Example, yesterday I measured 2.8 ppm and this afternoon around 1 p.m., I get 0 FC reading. I read somewhere once that if you find the FC reading is below 0.5 you should immediately shock the pool but that would take a boat load of bleach (which is hard to come by in rural VT) and I hesitate to use the 1 lb. bags of "shock" because I know that adds more CYA. Since the water looks beautiful, I don't want to take any steps which are overkill (not ready to drain to reduce CYA) but I'd like to be able to keep FC of at least 1 ppm without having to pour in an entire jug of bleach on a daily basis.

I heard from our friend, a pool installer/servicer, that he's heard a lot of complaints this summer of people who can't keep a FC reading. I also had a new VS pump installed that runs more hours of the day at a lower RPM but this problem pre-dates the new pump.

Any suggestions on what could be causing my inability to get the FC higher with just the pucks? Or if I should do something different?

Try taking a cup of pool water and a cup of tap water and mix it well. Then use 7 ml of that mixture for your CYA test. Then multiply the result by 2. That will give you a rough measure of your CYA. If it is still near 100, try 2 parts tap to 1 part pool water and multiply by 3. Let us know.

Okay, today's readings:

FC 2.0
CC 0.5
Ph 7.2
Alk 110
CYA 60 x 2 = 120

Our house is on a well so tap water is well water. Do you think that has any affect on the CYA test when I use 50/50 tap/pool water? I have distilled water I could use if that makes a difference.

Naw, that should be good unless your water is real cloudy.

Do not use any more pucks or bags of shock. They will just raise your CYA!!!

To get your pool sanitary and keep algae away, you will need to maintain an FC of around 13 with a CYA of 120.

In your size pool, it will take 1 quart of 8.25% bleach to raise FC by 1ppm. If your loss is 2ppm per day, then you would need a half gallon a day.

Okay, thanks FormerBromineUser. Some questions to clarify:

In order to get my pool to FC of 13, I assume I would have to add approximately 416 ounces of 8.25% bleach (13 x 32 oz). Then, in order to maintain a level of 13 ppm, I would need to figure out how much I lose per day and add that back.

Once I add the approximately 416 ounces, how long is appropriate to wait to measure FC to ensure I have it in the target range?

Also, should I worry about what is causing the 2 ppm per day loss or not?

Yes, once you add that amount, you can test about an hour later to see if you hit your target.

A 2ppm daily loss is about average, so no, I wouldn't worry if it stays around there. As the temps cool down, you will lose less. As bather load increases, you will lose more. Test FC daily until you get to know the pool at 13ppm.