Black Algae, Wire Brush, New Plaster

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So 1.5 hours later the reading went down from FC 15 to FC 14 with only three bathers in the pool for less than an hour. Perhaps I should've used more than the normal amount (two level scoops) of R-0870 powder? Or perhaps the brushing of the pool during that 1.5 hours gave the chlorine something to consume?
 
I added another gallon of 12.5% bleach, waited an hour and the FC was still only 17.5. So I removed all the June bugs from the skimmer thinking they may be part of the problem.

I closed the pool at 10:50pm, turned off the SWG and added another gallon of 12.5%. I'll wait till 11:50pm to check FC again, and then perhaps add another gallon at that time depending on the reading.
 
Oops I fell asleep before the midnight reading. This morning's readings are as follows.

FC 16
CC 0.5

So something used up a gallon of 12.5% bleach overnight. I added another gallon. Then 30+ minutes later I checked again.

FC 19

Can someone please tell me how adding a gallon of new and fresh 12.5% bleach to a clear 15,000 gallon pool only adds 3ppm?
 
edjanowsky said:
Oops I fell asleep before the midnight reading. This morning's readings are as follows.

FC 16
CC 0.5

So something used up a gallon of 12.5% bleach overnight. I added another gallon. Then 30+ minutes later I checked again.

FC 19

Can someone please tell me how adding a gallon of new and fresh 12.5% bleach to a clear 15,000 gallon pool only adds 3ppm?
Click to expand...

I added another gallon of 12.5%, turned the SWG on at 100%, waited 30 minutes while brushing the pool and checked again.

FC 21
CC 0

Can someone please tell me how adding a gallon of new and fresh 12.5% bleach to a clear 15,000 gallon pool only added 2ppm this time?
 
chem geek said:
If you want to see how much chlorine it will take in your pool before chlorine starts to hold, take a 2 gallon bucket of pool water and add 6% bleach to it where 1/4 teaspoon will be 10 ppm FC. Add the chlorine, mix, and test in an hour. If the chlorine has mostly been used up, then add some more, mix, retest in an hour. Repeat until the chlorine mostly holds. That will give you an idea of how much chlorine will be needed (scaled up for your pool, of course).
Click to expand...

I'm thinking I need to do this. Any thoughts?
 
Did you get a bad or old batch of chlorine? Are you storing it inside? High temps and sunshine will degrade chlorine quickly. 12.5% bleach will degrade faster than 8.25% bleach.

If you had black algae on your walls, brushing could have used up a lot of the bleach.

Another thing to consider is that people on public pool tend to "p" and that means ammonia which will instantly use up chlorine.

Another thing to consider is that certain types of bacteria will convert CYA into ammonia. Have you checked your CYA lately?
 
Thanks Karen!

I'm storing it in the pump house. I bought 8 gallons from the PS yesterday where they store it in a non-climatized warehouse. However it seems new. The date code is 144-17 so it was made in April. If there's a simple way to test it, I'll do it.

I considered the algae from brushing the walls but that and pee aren't really a factor overnight.

CYA was 60 yesterday by glancing.

All these variables are really starting to wear me out.
 
Running a resident pool can be a hassle and running a commercial pool has to be very frustrating. April bleach is actual quite old (4 months), especially at 12.5% and especially if they store it in a non-temperature controlled environment. I have residential pool and I used to be a "jug tosser" and manually used liquid chlorine as my primary source. I used about 3/4 of a jug of 8.25% a day. I found Wal-Mart generic 8.25% bleach to be the freshest and cheapest. They sometimes carry 10% in the pool isle but it can be hit or miss on freshness.

This website lists bleach half-life: http://www.odysseymanufacturing.com/about_product.htm

The website doesn't list your exact %, but you get the idea. Not a very accurate estimate, but it seems that stored at 90 degrees, your 12.5% will be half strength after 90 days.
 

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This morning's readings are as follows.

FC 21
CC 0

I'll try to keep it at this level today. I turned the SWG back on to 100% and added 28oz of MA.

Pool math makes it look as if my 12.5% bleach is only about 8.5% strength. Two gallons raised my 15000 gallon pool's FC from 14.5 to 26.

I have a sand filter.
 

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