Must not have shocked properly... green again

[Bubba17]

Started shocking with Cal Hypo on July 3rd. Yeah, I was real popular on 4th of July. It was green and cloudy so nobody was going swimming anyway. Had FC up to 18.5 (with CYA around 45 at that point) and it held overnight, so I let it come back down. The green went away but the cloudiness never did. I've been brushing twice a day and backwashed a few times. After a week I could almost see the bottom drain again and then the green started to come back. I never let the FC go below 6.0. While vacuuming every square inch of the pool yesterday, I could tell it wasn't dead algae, which sucks up like dust, but still growing, requiring me to scrub hard with the vacuum head. I'm guessing mustard algae from reading other stories. It will kick up a green cloud if you brush it, and it loves the shady side, slightly more than the sunny side. You can see big green swirls on the bottom where the water circulates. Funny thing is the FC level has been holding overnight since this problem started. I've been testing morning and night, before and after the sun hits it. It loses 3-4 ppm FC during a sunny day.

Anyway, looks like I need to shock again. CH is low so I can use Cal Hypo. pH is on the high side so I'm guessing I need to bring it down. I read not to trust pH readings while shocking, and CYA readings when it's cloudy, so what to do first? These numbers should be good as they have been consistent and responded as expected when adding chemicals, regardless of the cloudiness.

FC 8.0 (this morning, will be 4-5 this evening but I knew I would be shocking)
CC 0
TC 8.0
pH 7.6
TA 70
CH 70
CYA 40

I plan to add MA first to bring down the pH. Pool Calc says 2 quarts to get to 7.0. Can I add it all at once? How long to wait before hitting it with Cal Hypo? Test again or just shock it?

I plan to use Cal Hypo to get the FC up to 24, brush it and check FC tonight, check FC and brush it again in the morning, then run the power cover over it to keep the sun out. Probably uncover it in the evening, test FC, brush it, etc. etc. How many days of this am I in for? I'd like to think we can swim next weekend but the math ain't working out.

Any other suggestions?

If this doesn't work, 27500 gallons = 136 cubic yards, of dirt that is. Here's a handy volume converter:

http://www.convert-me.com/en/convert/volume

Thanks for any advice.

 

[duraleigh]

How many days of this am I in for? I'd like to think we can swim next weekend but the math ain't working out.

Clearing a pool with algae is a process...not an event. I've always liked chem geeks criteria..........

The process is complete when:
A. You hold FC loss to 1.0 or less overnite
B. Your CC's test .5 or less
C. Your water is sparkling

Until you meet those three goals, keep your FC at shock level, backwash as necessary, brush often and run the pump 24/7. You will clear your pool.

 

[JasonLion]

You should lower your PH, but don't make that large of a PH change all at once. I would bring the PH down half to 2/3rds of the way, wait an hour, test the PH again to see where you are, and adjust from there.

 

[frustratedpoolmom]

Maybe I'm missing something but why should he lower the ph? 7.6 is ideal, not high....?

If it is mustard algae, which doesn't have a green tint, I don't think? But if it is, I read it's resistant to higher FC levels. So after your done shocking it might be good to run higher levels, like 7ppm for a while. In any event, I think it's safe for you to shock to 24 which is the recommend level for mustard for a CYA of 40, and hold it there as Dave advised, until you meet the three criteria he stated.

 

[Bubba17]

Keep FC at 24 until it's sparkling? Holy cow... the water gets too chilly after Labor Day or so. Just kidding. It hasn't been sparkling in months. I've never lost more than 0.5 overnight during the first shock process, so I'm thinking I'll meet that tonight. CC hasn't been more than 0.5 since I got my TF-100 kit. Only problem is the cloudiness. I suspect I might need to replace the sand in the filter. It's been there since we bought the house in 2001. Owners before us replaced the filter due to a tree falling in approx. 1999. I was hoping I could wait until the end of the season, not wanting to shut it down for any length of time.

I'm going to add a quart of MA right now and give it an hour. Thanks for all the help.

 

[frustratedpoolmom]

Keep FC at 24 until it's sparkling? Holy cow... the water gets too chilly after Labor Day or so. Just kidding. It hasn't been sparkling in months. I've never lost more than 0.5 overnight during the first shock process, so I'm thinking I'll meet that tonight. CC hasn't been more than 0.5 since I got my TF-100 kit. Only problem is the cloudiness. I suspect I might need to replace the sand in the filter. It's been there since we bought the house in 2001. Owners before us replaced the filter due to a tree falling in approx. 1999. I was hoping I could wait until the end of the season, not wanting to shut it down for any length of time.

I'm going to add a quart of MA right now and give it an hour. Thanks for all the help.

Tell me again, why do you want to lower your PH?

I'd say replacing the sand is a great idea...

Maybe I'm reaching here, but I think it's a good possibility that the numbers weren't accurate, your CYA may have been higher than you thought, and the FC lower than you wanted and the algae wasn't completely dead....

In any event good luck Hope it clears soon!

 

[Bubba17]

From what I've read here, the chlorine works better at 7.0-7.2. I must have read it on either the Shock or Algae articles in Pool School. (Of course I can't find it now.) I hope I'm not confusing it with aerating to lower TA. I understand that works LOTS better at lower pH. Correct me if I'm wrong... I'm getting ready to put the 2nd quart of MA in... first quart brought the pH down to 7.3 exactly as expected. Thanks!

 

[chem geek]

If one is going to shock with lots of chlorine (near 20 ppm or more FC) then it is better to lower the pH some before starting. For example, if one has 45 ppm CYA and 100 ppm TA and a pH of 7.5, then adding enough chlorine for an increase of 18.5 ppm FC would raise the pH to 8.41 for an "active" chlorine concentration of 0.23. If one instead first lowers the pH to 7.2, then the added chlorine raises the pH to 7.76 and the "active" chlorine amount is 0.29 which is closer to the intended shock level (which is 0.3). It's not a huge deal, but you can see that it does make a difference.

Richard

 

[frustratedpoolmom]

If one is going to shock with lots of chlorine (near 20 ppm or more FC) then it is better to lower the pH some before starting. For example, if one has 45 ppm CYA and 100 ppm TA and a pH of 7.5, then adding enough chlorine for an increase of 18.5 ppm FC would raise the pH to 8.41 for an "active" chlorine concentration of 0.23. If one instead first lowers the pH to 7.2, then the added chlorine raises the pH to 7.76 and the "active" chlorine amount is 0.29 which is closer to the intended shock level (which is 0.3). It's not a huge deal, but you can see that it does make a difference.

Richard

Thanks Richard, excellent info!!!

 

[Bubba17]

Been keeping FC in the mid-20s since Sunday night, and I think the cloudiness has gotten worse. I'm adding bleach in the morning since it's easier to deal with before work. I thought it was clearing up but I added 3 lbs. of Cal Hypo last night and it's much cloudier today. Could this be from the Cal Hypo, bleach, or combination? Should I stick with one or the other? I still get a bit of a green cloud when I brush, but it's less each time. It's using about 1 ppm FC overnight, although it's harder to see the changeover in color with the FAS/DPD test at the higher chlorine level. At lower levels I was seeing a very distinct color change from pink to clear, but at FC 25, it goes from pink to dark red, to a sort of dingy off-white (?), but never really clear. Does this tell anybody anything? I ordered more R-0871 yesterday. You really go through a bottle using 50 drops at a time!

 

[TripleB4me]

I'm certainly no sand filter expert but I've got to believe that after 7 years the inside of that filter has got to be a mess.

 

[JasonLion]

Usually all you have to do with an old sand filter is open it up and check the condition of the sand every two or three years. Often enough it will still be in great condition and you can continue to use it. If it has gotten very clumped/scaled and the clumps don't break up easily by hand then it needs to be replaced.

Some people prefer to replace their sand every seven years. New sand will filter somewhat better than older sand. Personally, I just add a little DE to the old sand and it filters better than new sand alone would filter.

 

[Butterfly]

From what I've read here, the chlorine works better at 7.0-7.2. I must have read it on either the Shock or Algae articles in Pool School. (Of course I can't find it now.) I hope I'm not confusing it with aerating to lower TA. I understand that works LOTS better at lower pH. Correct me if I'm wrong... I'm getting ready to put the 2nd quart of MA in... first quart brought the pH down to 7.3 exactly as expected. Thanks!

Here is probably where you read it: turning-your-green-swamp-back-into-a-sparking-oasis-t4147.html

 

[JasonLion]

Chlorine is significantly more effective at low PH only when there isn't any CYA in the pool. Once you have CYA in the pool, any PH value in the normal range (7.2 to 7.8) is fine. Extremely high (>8.4) or extremely low PH (<6.6) can cause chlorine to be ineffective. There are also some interesting secondary effects that can cause chlorine to be more effective at higher PH values. For example PH around 7.8 to 8.0 can favor the creation of monochloramine, which continues to kill algae even as the FC gets used up.

Despite all this, I often recommend lowering PH a little before shocking because many pools tend to drift towards higher PH. You can't easily test the PH while at shock level, so you want to insure that the PH will remain reasonable for the entire time you are shocking. If your pool has rising PH then you want to lower the PH before you start, so it is still reasonable by the time you finish.

Another effect becomes important when shocking with bleach at high CYA levels. Adding bleach raises the PH, which then comes down again as the chlorine gets used up. At higher CYA levels you need to add a large amount of bleach, which can raise the PH significantly. In these cases it is best to lower the PH a bit before starting, so the PH level after you add bleach doesn't cause scaling or metal stains.

The reasoning is different for pools with out any CYA. Around here that normally only comes up during baquacil conversions. Then it is important to get the PH to the low end of the range (7.2 to 7.4) before shocking because the chlorine is more effective at lower PH when there isn't any CYA.

 

[Bubba17]

Thanks for all the replies. Any ideas why it's still so cloudy, and got worse when I added Cal Hypo? I haven't tested everything since Sunday, before I started shocking. I've only added MA, Cal Hypo, and bleach. CH might be a tad higher, but TA and CYA should be about the same. Here they are again:

FC 25.0
CC 0
TC 25
pH 7.7
TA 70 (est.)
CH 70+ (est.)
CYA 40 (est.)

I take the multi-port valve off the sand filter at the end of the season, just to have a look, as I'm draining it. I've never seen anything of concern. The only thing I will mention, however, is that I get a few grains of sand out the port when I backwash. I've written this off to being the smaller grains getting lifted out. Should I be concerned? Hopefully this doesn't mean I've lost pounds and pounds of sand over the years.

 

[JasonLion]

It would be helpful to have good current test results for TA, CH, and CYA. Adding cal-hypo can cause calcium clouding. But, we need current TA, CH, and CYA numbers to be able to tell if that is likely or not.

 

[Bubba17]

OK, here is a full set of test results as of this evening:

FC 26
CC 0
TC 26
pH 7.6
TA 60
CH 100
CYA 45

Should I be holding the FC a bit higher to shock with 45 CYA?

 

[duraleigh]

Should I be holding the FC a bit higher to shock with 45 CYA?

No, you're fine.

Now, be sure to retest your FC tomorrow morning (don't add anymore 'til you test) before the sun gets on the pool....just FC.....you're looking to see if your FC drops 1.0 or less overnight. Any larger drop will indicate the presence of organics (algae).

 

[JasonLion]

With those numbers the clouding is extremely unlikely to be calcium related.