Algae killed but water still green

[baip]

We often open our pool late (just did it last Sunday) and typically find the water green. We would then use the SLAM method until free chlorine maintains overnight two days in a row. However, the water would still be very green at this point and we cannot see the bottom at the deep end. In past years we used flocculant, which requires running the pump in recirculation mode for two hours, stopping the pump for eight hours, and finally vacuuming to waste. This worked great but used a lot of water and heavy physical efforts because we wanted to vacuum fast.

I'm curious if there is any alternative method to clean up the pool. We have a sand filter and this year we tried clarifier without flocculant, but now 1 qt clarifier used (we did four treatments of 6, 6, 10, 10 ounces) and six days later, the pool looks almost as green as before. Clarifier did increase the filter pressure by more than 10 psi overnight (compared to 1-2 psi without) but the effect of one treatment is probably just a single day. We are continuing to maintain FC at the recommended level and FC does not drop overnight, so it's just fine dead algae.

I read about diatomaceous earth. How much do people usually add? Do I just add DE on top of existing sand or do I have to remove some of the sand (i.e., is there a limit to how full the filter can be filled)? How often do I need to remove / replace the DE layer?

Any other recommendations?

 

[mknauss]

Follow the SLAM Process

Floc and clarifier are not helping you. They have most likely compromised your sand filter media. Deep clean and most likely change your sand.

 

[woodyp]

Usually a couple of cups of DE. Add 1/2 cup at a time thru skimmer.....watch the pressure. Then the next 1/2 cup.

 

[baip]

Follow the SLAM Process

Floc and clarifier are not helping you. They have most likely compromised your sand filter media. Deep clean and most likely change your sand.

We changed the sand in 2019 (bought the house in 2018). And we have been following the SLAM process but I remember that more than 10 days passed the water still didn't clear up, which was why we tried using flocculant. This same situation happened again in 2020. Apart from pool opening, the sand filter appears to do a great job.

 

[baip]

Usually a couple of cups of DE. Add 1/2 cup at a time thru skimmer.....watch the pressure. Then the next 1/2 cup.

Got it, but do I just let DE accumulate on top of existing sand? Could you recommend a link that describe what to watch for (e.g., regarding pressure) and how to decide how many cups of DE to add?

 

[mknauss]

And we have been following the SLAM process

You are done when:​

• CC is 0.5 or lower;
• You pass an OCLT (ie overnight FC loss test shows a loss of 1.0 ppm or less);
• And the water is clear.

When all three are true, you are done SLAMing and can allow the FC to drift down to normal levels.

 

[baip]

We changed the sand in 2019 (bought the house in 2018). And we have been following the SLAM process but I remember that more than 10 days passed the water still didn't clear up, which was why we tried using flocculant. This same situation happened again in 2020. Apart from pool opening, the sand filter appears to do a great job.

Currently we have CC of 0.5 or lower and overnight FC loss of 1.0 ppm or less, but clearly the water is not yet clear. Strictly speaking, SLAM isn't done but given the speed the water clears, this uses a lot of chlorine, which we did in 2019, but chlorine is difficult to come by this year.

 

[baip]

You are done when:​

• CC is 0.5 or lower;
• You pass an OCLT (ie overnight FC loss test shows a loss of 1.0 ppm or less);
• And the water is clear.

When all three are true, you are done SLAMing and can allow the FC to drift down to normal levels.

Thanks. I was just reviewing the SLAM process and posted an update I'm curious why we have to maintain high FC when all algae is dead? We're now maintaining lower FC level but there is no loss overnight. Not to doubt the tried and true SLAM process, but trying to understand why.

In 2019 we dumped a large amount of chlorine daily for more than a week to very slow effects until we used flocculant. In 2020 we directly went for flocculant after the first two criteria were satisfied. In both years, after flocculant was used, the water cleared up very fast and we could just continue to maintain normal FC levels without algae problems.

 

[mknauss]

If all the algae is dead, SLAM level FC is not hard to maintain. You might use a little more chlorine each day over maintenance, but very little.
You can use Floc if you want. TFPC does not endorse its use. Just follow the SLAM Process. Use DE in your sand filter to assist.

 

[woodyp]

In your defense.......a sand filter is the SLOWEST type to be able to clear a pool.

 

[baip]

If all the algae is dead, SLAM level FC is not hard to maintain. You might use a little more chlorine each day over maintenance, but very little.
You can use Floc if you want. TFPC does not endorse its use. Just follow the SLAM Process. Use DE in your sand filter to assist.

I got your point regarding the use of flocculant.

During the day FC drops from 16 to 4--6 on a sunny day, with a 27000 gal pool this uses a decent amount of chlorine daily. Strangely, FC drops from 6 to 4 daily while not SLAMing. I don't know how to think about this if we assume the rate constant of chlorine consumption is independent of the (very low) concentration of hypochlorite in the pool.

 

[mknauss]

During the day FC drops from 16 to 4--6 on a sunny day

With that drop, there is organics in the pool water or your CYA is lower than you are using.

 

[baip]

With that drop, there is organics in the pool water or your CYA is lower than you are using.

I'm not trying to argue. There are perhaps some unaccounted for real-life complications. Just to provide my data points: 1) FC holds overnights; 2) We use Taylor K-2006, having used two different batches of CYA reagents.

Point (1) shows that FC is not oxidizing anything at night. If it was wrong CYA level (i.e., both batches of CYA reagent are somehow bad, possible though not likely), my point is: when we use normal FC levels, it should still decrease by the same ratio; i.e., roughly a factor of 3 (16 divided by 5), so FC should drop from 6 to 2.

In any case, we were able to use the same test kit to maintain good water quality after pool opening, and if somehow we lapsed, we were able to SLAM and quickly got back to normal (unlike in 2018 when we were following pool store's reports). So we are very much a believer in the SLAM process. Just for the pool opening process we made some adaptations to reduce a bit of chlorine usage.

Perhaps sand filter is to blame or the sand quality is not good.

 

[mknauss]

Great. I just want to be sure any new member that comes along this thread does not believe the SLAM process is go part way and use Floc.
You are welcome to do as you please.

 

[clambert1273]

I think by your arguments that you are just wanting to do it your own way & wanting TFP to agree and I don't see that happening... I have slammed many times without any issues & so have others. The one thing I caught from your post is opening late & that would seem to be the denominator in your problems.. I don't ever have to open or close but I still have to slam & prep pool for season early which for me is usually feb/Mar I start cleanup

 

[baip]

Great. I just want to be sure any new member that comes along this thread does not believe the SLAM process is go part way and use Floc.
You are welcome to do as you please.

So to clarify, if we were to continue SLAM until water is clear, the only way to speed up sand filter is to add DE?

 

[baip]

I think by your arguments that you are just wanting to do it your own way & wanting TFP to agree and I don't see that happening... I have slammed many times without any issues & so have others. The one thing I caught from your post is opening late & that would seem to be the denominator in your problems.. I don't ever have to open or close but I still have to slam & prep pool for season early which for me is usually feb/Mar I start cleanup

Sorry if my arguments sounded that way. I'm sure there are good reasons why SLAM, designed this way, works. I can see the why for the first two stopping criteria, I'm just not understanding the 3rd criteria. Even so, I follow SLAM precisely except for pool opening. Empirically, again for pool opening only, at least for me, maintaining SLAM levels of chlorine until water clears does not seem to speed up the process. This was based on my observations in 2019 alone, but I can't find enough chlorine to try again this year.

 

[clambert1273]

Sorry if my arguments sounded that way. I'm sure there are good reasons why SLAM, designed this way, works. I can see the why for the first two stopping criteria, I'm just not understanding the 3rd criteria. Even so, I follow SLAM precisely except for pool opening. Empirically, again for pool opening only, at least for me, maintaining SLAM levels of chlorine until water clears does not seem to speed up the process. This was based on my observations in 2019 alone, but I can't find enough chlorine to try again this year.

It's not to "speed up" process the reasoning is that until it is clear if you stop it can possibly cycle again - ask me how I know

 

[baip]

It's not to "speed up" process the reasoning is that until it is clear if you stop it can possibly cycle again - ask me how I know

Ah ok. We do continue to monitor overnight FC loss. Perhaps it is the sand filter making this process very slow for us. When we vacuumed (before using flocculant or clarifier), we could see return water being green, meaning that the dead algae was very fine and ran through the filter unimpeded.

 

[mknauss]

So to clarify, if we were to continue SLAM until water is clear, the only way to speed up sand filter is to add DE?

Correct. And deep clean the filter if any floc or clarifiers have been used. Floc normally means the sand should be replaced.