algae and high ph

[dalejanus]

I have 24ft ag vinyl pool, about 12000 gallons.

I have an algae problem so I am shocking the pool.

But before I started, I was surprised to see my ph at 8.2. It has always stayed at 7.2 for the last 3 years.

my numbers
fc 8.5
cc .5
ph 8.2
alk 90
cya 20


I was going to wait until I got rid of the algae before I started worrying about the ph. I was just surprised that ph went way up.

I added 2 3/4 jugs of bleach after this reading that should get me up to 16ppm

I will keep the fc up and hopefully that will get rid of the algae. I only have a week or two of swimming anyway. (water temp is 76 today). Which is also why I'm not going to bother increasing my cya.


Anyway, I'm interested in hearing about why my ph went up from all you experts.

---Dale

[chem geek]

First of all, are you sure you have an algae problem? It is unlikely that at the high chlorine levels (relative to your 20 ppm CYA) you have algae. If your chlorine levels hold overnight, then you most likely do not have algae (so do they hold overnight?). If the water is cloudy, then this would be due to the very high pH over-saturating the water with calcium carbonate. This depends on the Calcium Hardness (CH) which you did not report, but even with a CH of 200 you might start to see some cloudiness and very likely at a CH of 300 -- again, due to the very high pH.

As for the cause of the pH rise, how rapidly did this occur (i.e. how often did you check the pH)? The pH will tend to rise in pools with high TA, but your TA isn't particularly high. If there was lots of aeration (including raindrops), it could have gone up, but usually not as high as 8.2. Were any chemicals besides chlorine added recently? Are you using only bleach or chlorinating liquid or are you also using Cal-Hypo for chlorine?

If the chlorine holds overnight, I would try lowering the pH first. Even if the pool had a green cast to it, that could be copper in the pool since the very high pH would force it to color the water green (from copper carbonate). Again, the overnight chlorine test is the easiest way to know if it's algae or something else.

Richard

[dalejanus]

I failed to mention that we did not add any chlorine for a week because it was raining like heck every day for a week. Then we let it go for a few more days. (I know, I know) So I am pretty sure it is algae. It's green.

We went about a week and a half with out testing. I don't check calcium very often with a vinyl pool, but I'll check it tonight to be sure.

No chemicals added except bleach. Well, I think my daughter put in a floculate (stuff that clumps things together) that my wife bought at the beginning of the season, but nothing else.

I will get an overnight chlorine to see if it is holding. Once it is holding, I will lower pH. I think I still have some muratic acid with my pool stuff.

Thanks.

[aylad]

No chemicals added except bleach. Well, I think my daughter put in a floculate (stuff that clumps things together) that my wife bought at the beginning of the season, but nothing else.

Keep in mind that high chlorine levels tend to give false high pH readings. I would retest your pH when your chlorine comes back down to its normal levels before using acid to lower it.

Janet

[dalejanus]

here are my numbers from last night
fc 13.5
cc 1
ph 8.2
ta 100
cal 80
cya seems to be 0, I could always see the black dot.


We vacumed to waste last night.


This morning fc 12 and c .5


I found my muratic acid, but I can wait to put it it.

The ph was 8.2 before I started shocking.

Still green this morning, can't see the bottom.

---Dale

[dalejanus]

The pool is somewhat less green, but I'm having vacuum trouble. It doesn't always want to seal at the skimmer and since I can't see the bottom (today I can see if faintly) I was not able to tell if I was vacuuming or just brushing stuff around. Then the pin that attaches the head to the pole broke. Of course this is at 7:30pm, so I run to the pool store before they close. Pool store is closed on Wednesdays. Sigh.

So I shocked some more, now up to 25 ppm (a little more than I planned). We'll see how much it drops overnight.


When should I add Muratic acid to bring PH down? After algae is gone or do it now?

[aylad]

When should I add Muratic acid to bring PH down? After algae is gone or do it now?

Your chlorine is going to be more effective at the lower pH ranges, so bringing it down now would be fine...as long as you know your levels are accurate. High chlorine (I'd say above 10) will skew your pH test results upward, so just be careful not to drop it below 7.0. I'd shoot for 7.4 while your chlorine is high just to give you a little wiggle room.

janet

[dalejanus]

good advice, aim for the middle.

Bleach calculator says 9oz for a .2 decrease, I'll try 27 oz which should bring me from 8.2 to to 7.6 or so.

As everyone on this forum says, small steps are much better than large ones.

The pool is clearing, now its blue rather than green.

[aylad]

The pool is clearing, now its blue rather than green.

That's good news...just keep the chlorine and patience level up, and you'll be crystal clear before long!

Janet