7.2 vs >8.2 Grrrrrrrrrrr

[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!

[Infidel]

I suspect the CYA levels are higher then I thought, as the last test indicated. Since my Cl readings are so variable, I'm sticking to a schedule of adding 12.5ppm Cl every 12 hours (8am, 8pm). This should hopefully maintain at shock level long enough.

The pump is running 24/7, not backwashing though due to the pressure in the filter tank not being elevated. Pool Co. out to give me a quote on replaster yesterday indicated that my sand filter may need cleaning if I've got lots of algae that is difficult to remove. Any truth to that?

[duraleigh]

Backwashing cleans your filter and sand....that's all you need. You may backwash anytime you like but I always look for a pressure rise first.

That 12.5ppm worries me a bit. How do you know that? It sounds more like you are putting in 12.5% Cl which may or not relate to ppm. How big is this pool (gallons)? If it's 10k, I understand. If it's not, you need to recalculate.

[brent.roberts]

I want to encourage you to check and top up the chlorine more frequently than every 12 hours.

Here's what can happen.

At 7:00 PM you top you your chlorine to say 20ppm. If there is a lot of algae
in the pool it can be down to 8 or 10 PPM in 2 hours. After 4 hours the level is so low that it starts growing and reproducing again. By the time you get up the next morning at 7:00 AM to top it off, you are back to the same pea soup you had when you went to bed.

Now you top up at 7:00 AM and you have the whole day's sunlight to kick the h*** out of the chlorine along with the algae basking in the sun and reproducing.

Try to shorten the cycle. Initially topping up every couple hours could be quite important. As the algae concentrations go down, the yo-yo of your chlorine levels will slow down and you can relax the schedule a bit, but you've got to break the back of the chlorine.

Do you have a reliable CYA measurement yet ??

[Infidel]

Part of the problem with checking the Cl is that I have pretty wide margin of error due to dilution, I'm probably looking at +/- 20ppm when I look at the comparator and the color is between the 3 and 5, and I'm at a 5x or 10x dilution. I could have 10-15ppm of Cl consumed immediately and not be able to detect it on the test kit.

I'm using the poolcalc to determine the 12.5ppm, it's more like an 8K gallon pool, I'm using 6% bleach in 1.7 gal jugs ~12.5ppm addition/jug.

I agree that the free Cl could be consumed within a few hours, leaving me below the breakpoint/shock level for too long. I'll add more frequently. I know the consequences of not enough Cl, but I'm not sure there are any bad things that can happen if I over chlorinate. With my high CYA and organic issue I think that a high Cl condition wouldn't persist very long. Wife and kid swam today with elevated Cl with no issues, about 4 hours after the last 12.5ppm addition, there's actually not a lot of Cl odor either. It's either getting consumed breaking down organics or it's not available due to pH or CYA issues. Ph is maintaining around 7.2.

[Infidel]

A 22.5ppm jolt this am leaving for work, nice and blue by the time I got home.

[brent.roberts]

congrats !!

you've almost earned your stripes as a true beleiver in the BBB method.

keep the filtering going and hold the CL pretty high for a couple more days

Brush it everywhere to uncover any living algae that may be hiding under a layer of dead slime.

Next week you need to get a handle on the high level of CYA.
I don't recall if you were using stabilized chlorine ( pucks or tablets ) that continually add CYA, but it is a pretty common trap. The CYA keeps going up and the owner sees the CL levels at 3 to 5 and thinks everything is just dandy.
Then the frog pond hits and until you learn that CYA at 100 or more is counter-productive, nothing clears up the algae ( for very long )

The other good news about all this is that the algae ran up the red flag. If algae can grow, so can the nasty bacteria that may make you and the kids sick. Coliform can flourish in the same soup as algae and if the pool didn't go green you might had a rough time until the connection got made that the pool was the source of the infections.

Keep it up. If you need help on a few trick to get the CYA down, there are lots of good folks here to help