7.2 vs >8.2 Grrrrrrrrrrr

[duraleigh]

Anybody can write anything they want and post it on the net. Nevertheless, This excerpt was taken from an article about chlorine that seemed quite believable and well thought out. It should answer your questions about the relationship of Cl and pH

The amount of hypochlorous acid and hypochlorite ion that is produced when chlorine is added to the water is directly related to the pH of the water. At a pH of 6.0, 96% of the chlorine will become the desired "killing" form of chlorine, hypochlorous acid. At a pH of 7.0, 75% of the chlorine will become hypochlorous acid and at 8.0 the hypochlorous acid concentration is only 25%. At a pH of 7.5 (the average spa) the amount of hypochlorous acid produced is about 50%.

[waterbear]

Anybody can write anything they want and post it on the net. Nevertheless, This excerpt was taken from an article about chlorine that seemed quite believable and well thought out. It should answer your questions about the relationship of Cl and pH

Pretty much true. The ratio of any weak acid to it's corresponding ion (in this case hypochorous acid/hypochorite ions) is pretty much pH dependant!

[Poolsean]

"Lack of Cl will allow algae to grow, high pH will lock up the Cl making it innefective, which is why I have 25ppm Cl with no affect. The Taylor kit doesn't appear to be accurate but I'm not sure what damage low pH would cause with regard to algae."

With the high chlorine and no affect on the algae, you're probably dealing with high phosphates as well, which is just allowing the algae to feast in your pool. Check and treat for phosphates.

[waterbear]

Good point Sean, This might be one of the cases where phosphate removers are actually called for. Test your phosphate leves and also test your nitrate levels. If phosphates are high and nitrates are low then phosphate remover might work for you!

[Infidel]

Thanks for all the info. Here's some background:

Alk 120 (consistent with reading 2 wks ago)
Ca 350 (consistent with reading 2 wks ago)
CYA ~100+ from reading tonight, has been reading 72-80 last 2 wks
pH 7.6 OTO / <7 Taylor (as of 2am Texas time)

Cl is being read from the Taylor at 1:5, color is usually between the 3 and 5.
I'll grab a pH meter from work tomorrow and start checking the "real" pH and see what method is accurate. I use the K-2005 kit from Taylor.

Are you sure 6-8 ppm is suitable for lime green pool with CYA ~80? WIth regards to consistent concentration, I'm unable to distinguish between the 3 and 5 (15-25 ppm) on the color comparator, so if it's yoyoing, it's doing it between 15-25, which should be sufficient to keep things killed, even at the low point in the cycle, correct?

The pool is looking less green since adding acid 4-5 hrs ago. The low pH should be increasing the %hypochlorus according to Duraleigh's excerpt, which appears to be occurring. So, algae in spite of high Cl, may indicate pH is elevated and the active Cl isn't present in great enough quantities it sounds like.

Are phosphate / nitrate commonly performed by pool stores?

[brent.roberts]

I've seen it posted here a number of times that the best range for PH when fighting algae is 7.2 to 7.2

The above explanation about ion levels shows why. So I think I'b be shooting
to get the PH to 7.2

To really get the kill going well, tonight, as soon as the sun is off the pool, dose it up to your shock level. Run the pump to circulate and re-test in an hour or so. If you see a big drop, dose it again, and keep doing that till you can't stay awake. This will cut the yo-yo out.

If the majority of the CL is consumed in the first couple hours after adding, the the algae can go right on growing again throughout a lot of the night. So check it every hour or so tonight.

Keep track of what it does and let us know.

[duraleigh]

I am watching this thread devolve (yes, that's the word I meant) into issues that I think are peripheral to the problem. Chlorine kills algae

If you still have algae in your pool, you have not brought your chlorine levels high enougn, long enough to get rid of it.

The solution is to bring your Cl level up to about 30-35ppm in the evening and then test your Cl the next AM. Whatever drop has occurred is the result of killing organisms. Bring your Cl right back up to that 30-35 level immediately. Hold your Cl at that level until your pool is clear and then let it drift back down into a maintenance range of around 5-10ppm.

If this fails, (and I've yet to see it fail on this forum) then I think you could safely assume you have another issue. You cannot tiptoe up to your algae problem....you must kick it straight in the butt with chlorine and kick it long enough to get the desired effect....a clear pool.

PS - If it's not clear, I am in complete agreement with Brent, I just like to use big letters more than he does.

[waterbear]

I've seen it posted here a number of times that the best range for PH when fighting algae is 7.2 to 7.2
actually, If you are fighting algae a pH of about 7.8 is beneficial because you will favor the formation of monochloramine, which is a very good algae killer. It is short lived, however so you will have a big chlorine demand.
The above explanation about ion levels shows why. So I think I'b be shooting
to get the PH to 7.2

To really get the kill going well, tonight, as soon as the sun is off the pool, dose it up to your shock level. Run the pump to circulate and re-test in an hour or so. If you see a big drop, dose it again, and keep doing that till you can't stay awake. This will cut the yo-yo out.

If the majority of the CL is consumed in the first couple hours after adding, the the algae can go right on growing again throughout a lot of the night. So check it every hour or so tonight.

Keep track of what it does and let us know.

Hope this is helpful! Also, I would double check your CYA levels. the test is the most subjective and it is possible that they are higher than you think they are. Your own testing hints to that! In that case you have probably not brought your pool up to a true shock level and kept it there long enough to kill the algae!