Stumped by persistent algae

I've had a pool since 1976 and have never encountered the problem I'm having now. I have always maintained my pool myself as far as testing and dosing of chemicals and normally have crystal clear water. I've had an algae problem that I can't seem to get rid of. I've tried several algaecides with no effect. Here are my test results FAC 5, TAC 5, CH 400, CYA 100, TA 110, pH 7.4, TDS 900, Water temp 76. I normally use a floater with 3" Trichlor tabs, and shock as needed with 68% Calcium Hypochlorite. I know the cyanuric is way too high and I've done some partial water changes to try and bring it down.
Any suggestions would be appreciated.

Yours is actually a problem that we see frequently from people who have used trichlor (or dichlor) for a long time. The problem is that your chlorine is not high enough based on that CYA reading and since 100 is the highest the CYA test can read, it may actually be much higher than that. Take a look at the Best Guess Chlorine Chart in my signature below for the correlation between CYA and needed chlorine levels.

I'd suggest just using bleach for your chlorine. Your calcium hardness is getting kind of high and your CYA is way too high and the trichlor tabs will continue to add more CYA.

You definitely need a better kit that can test values past 5ppm. Order a Taylor K-2006 or 2006C (better buy) from the test kit link in my signature. You'll need it to operate this high CYA pool.

Welcome to the Pool Forum!

You have 3 options:

1. As Watermom explained, you can operate with high CYA *if* you have high chlorine, possibly 15 ppm normally and 30 ppm while cleaning. BUT, you must be able to test accurately to do so.

2. You can drain and refill. I don't know how much you need to drain: usually a CYA reading of 100 *actually* means, "100 or higher". Your actual CYA may be 200! If you have a vinyl pool, this isn't really an option. Even with a fiberglass or concrete pool, it's not an option if your pool in level damp ground -- pools can literally float out of the ground.

3. You can add borax to reach 60 ppm, and phosphate removers to get PO4 < 125 ppb. This can make it much easier for the chlorine to kill the algae. But lowering phosphates can be difficult, since you may have high phosphates in your fill water, AND you may be in the habit of adding pool chemicals which CONTAIN phosphates!

Thanks for the comments, I've started with some partial water changes and after of week of this the pool is at least nice and blue now. Chlorine is at 0 but CYA is still at least 100. I'll continue the water changes and start dosing with some chlorine. Recommended test kit has been ordered. Should I use any stab. tabs in a floater. Thanks again for the comments.

No, you don't need any more CYA which is what stabilizer is. Yours is already too high which is why you are doing the partial water changes.

Got it, thanks.

Don't wait; start dosing with chlorine NOW! It is much, MUCH easier to avoid algae, than to clean it up. A single algae episode can consume a month's -- or in bad cases, a season's -- worth of chlorine!