phosphates and algae

[CarlD]

Hello all

If this topic has been discussed anywhere else in the forums, please direct me to the thread. We opened our pool last weekend, a 21ft AG round. Mustard algae patches have already returned. My current readings are as follows...

TC >15
FC> 15
CYA 99 too high, I know
pH 7.4
ALK 127

We are hitting it with shock, NOT using any sticks or pucks with stabilizer in an attempt to bring that 99 down.

1) As pointed out, you need to run your FC level up to 25 if you want to properly shock your pool. I don't know what you are using that is called "shock"--it could be all sorts of things. Many of the powder packets of "shock" are di-chlor--and they will also add CYA to your pool, making your problem worse. However, cal-hypo and lithium-based chlorinators won't add CYA--but they will add calcium or lithium. Depending on your calcium level, this may not be a problem--I have no idea what lithium does to water. "Shock" could also be liquid shock--usually sodium hypochlorite--same as bleach and sometimes even the same concentration as Ultra Bleach (6%). Liquid chlorine/liquid shock/bleach is normally the best to use with the least side effects.

2) Your attempt to bring the CYA of 99 down will fail. Sorry to be blunt. There are only two ways to lower CYA. The easiest is dilution--drain 50% of your water off and refill and your CYA should drop to 50ppm. You don't want to know the other way..... If you don't want to drain and refill plan on keeping your FC between 8 and 15ppm for normal use. This won't hurt you, but you may see your bathing suits fade a little--that's the worst side effect. If you have Ben's test kit or another FAS-DPD powder chlorine test kit, it's pretty easy to measure chlorine levels.

The pool water itself is clear. We run the pump 24/7, brush daily...etc. Last summer I battled the beast with not very good results. I am convinced I am growing a resisitant strain.

When I had my water tested yesterday, an additional test was run for phosphates. It took a little while but I was told that I had a high phosphate level of about 800 ppb. It was explained to me that phosphates act as an algae fertilizer and this might be why I have a resistant and recurrent algae problem. Of course it was recommended I use a phosphate remover but being an avid pool forum reader, I am reluctant to put additional chemicals in my pool.

So I ask your opinions about this. As always, I value what I learn here in the forum.

Thanks for your help!
Melba

Melba, try the other things suggested first. If you follow them with patience and persistance, they work 99.9% of the time. Only then, when you fall into the that 1 in a 1000 group should you move on to trying things like phosphate removers. They are generally pushed as a hi-tech, quick-fix, but that's just hype. There are no quick-fixes that don't boomerang in some way. I don't yet see any evidence of a chlorine-resistant strain of algae--your TC and FC are too low in relation to your CYA to kill an algae bloom. If after two weeks in an environment of CONSTANT FC=25 (at CYA=99) the algae is still there, maybe then you may need a "Plan B". But you aren't there yet.

The best way to get rid of algae is to extend what you are already doing, as has been suggested. Get FC up to 25, and keep it there, checking 2x to 3x/day and adding bleach as needed, run your filter 24/7. Brush your pool everyday, and vacuum to waste everyday. And be patient and persistent. Remember, if your FC drops too low, you are basically back to square one as the algae will start growing again.

Good luck!