have had trouble with algae...

[chem geek]

If you were in Arizona, perhaps, but not for New York. Full sun in New York doesn't have the sun as directly overhead as in places further south, but if you want to try shooting for 60 ppm then that might be a reasonable compromise. The thing is that it's a lot easier to add CYA than it is to lower it so if you are in a process of a partial drain/refill anyway, you might as well go lower to say 50 ppm since you can always easily add more CYA. Fresh water is also helpful pools generally since there are other things that accumulate besides CYA, though none of them are anywhere near as problematic as CYA. Up to you what to do -- just giving you the reasoning.

See this link (select "July" and "Horizontal Flat Plate") for a map of solar insolation on a horizontal surface to see that New York gets about 3/4ths the amount of sun as the southwestern U.S (June is even more extreme). Some of that is related to latitude since the sun is more directly overhead in the south but most of it is related to the very clear skies in the West compared to cloudier rainier summers in the Northeast.

 

[Richard320]

Also reading BBB for beginners it says "If you have a SWG or get extreme amounts of direct sunlight on the pool, adjust CYA to between 60 and 80. Otherwise adjust CYA to between 30 and 50"
My pool is in the sun no trees any where so shouldn't i be in 60-80 range not 30 :?:

You'll need to decide that for yourself.

I would caution you to wait until your algae problem is absolutely positively licked before you jack it up, or you'll be buying bleach by the pallet.

 

[rick6668]

Some very good advice in this thread. just want to add that your CYA level might be much higher than 100. The test in the TF100 really only goes to 100, and the pool store had a value of 200 (Usually the Pool Store's values for CYA are lower than actual).

I recommend that you use 1/2 pool water & 1/2 tap water for the CYA test and then multiply the results by 2. This will help let you know if you are over 100. If it is higher than 200, you might need to use 1/4 pool water and 3/4 tap and multiply by 4 to get an accurate reading. You definitely need to drain some water, sooner rather than later.

 

[Bama Rambler]

Just to clarify the cya is preventing my chlorine from staying in the water. So with not enough chlorine the algae will continue to return? Once i drain the pool and fill it up add chlorine until the fc=39. Am i on the right track?

NO the CYA isn't preventing the chlorine from staying in the water. It's preventing you from keeping enough chlorine in the water. The algae is what's preventing your chlorine from staying in the water. More correctly it's using up the chlorine at a rate greater than you're adding it.

Correct about "with not enough chlorine the algae will continue to return" part. You must keep your FC at shock level for your CYA in order to kill all the algae and once you've passed the OCLT you must keep your FC equal to or higher then the lowest recommended FC for your CYA.

You're a little off in your thinking. The amount of FC you need to maintain is directly related to the amount of CYA you have in the water. If you drain and refill, you will have zero CYA and therefore you only have to maintain 2 ppm FC in the water. There is a caveat to having zero CYA. The sun will burn off the FC almost as soon as you dump it in there with zero CYA in the water.

You need a little CYA (about 40 ppm) in the water to protect the FC from the sun.

 

[chem geek]

Think of it this way. Most of the chlorine you measure as Free Chlorine (FC) is actually bound to Cyanuric Acid (CYA) and is inactive. It's in reserve as in a reservoir that can replenish the small amount of unbound chlorine that is active. It is this small amount of active chlorine that actually kills algae.

An analogy is having soldiers on the front-line and are actively fighting the enemy, but where you have most of your soldiers behind these lines in reserve. The rate of killing the enemy has to do with how many active soldiers there are and has nothing to do with the size of the reserve. When a soldier gets killed from fighting (and kills an enemy soldier in the process), they can be replaced with one from the reserve, but again the rate of kill doesn't depend on the size of the reserve. The size of the reserve just tells you how long you will be able to fight, but not whether you are going to win the war.

The amount of active chlorine is related to the FC/CYA ratio so as the CYA level is higher the FC level has to be proportionately higher to get the same active chlorine level.

 

[Golddlocs]

Good analogy i had two heavy rains i did my cya test and got three different readings after the rain 80, 90, 80. :-|. I don't think i am suppose to get rain tonight so i will perform oclt test I figure it can't hurt. My water looks great its crystal clear. No algae, I ran my robotic yesterday and I guess it stirred up the chemicals because this morning it looked great. So we will see. I hate to dump the pool and refill because we only use the pool until the end of July and this year it has not been hot enough to use it that often so i thought i would lower it for the winter not more than 12 inches correct? And then wait until next summer, test my cya before i fill it back up :?: