Suddenly getting algae on pool floor. Why now?

[A_kraker99]

So our new pool has been up and running since early July. I have been keeping chemistry in check and have not had any problems till now. Twice in the last week I had to brush the bottom of the pool because of visible layer of algae. It has been raining a lot but I still kept the levels in check.
FC: 4-5 all week long
CC: 0
CYA: 40-50
Alk: 90
Ph: 7.7
Water temp:65 (yes, 65. I’m in Michigan)

Is it possible that with all the rain I’m just seeing dead organics settling that are unavoidable? I don’t understand it.

 

[mknauss]

Do a Overnight Chlorine Loss Test. That is a good way to see if you have active organics.

Does the material 'poof' away when you brush it?

 

[A_kraker99]

Do a Overnight Chlorine Loss Test. That is a good way to see if you have active organics.

Does the material 'poof' away when you brush it?

Yes. Like a cloud of dark green

 

[mknauss]

You can do the OCLT or just move right to SLAM. Should be quick with your cool water.

 

[A_kraker99]

This drives me crazy. I brought chlorine levels up to 11PPM on Thursday, which I guess is just under my shock level for a CYA level of 40. It was at a minimum of 11PPM all weekend down to about 7PPM today with some constant additions each day. Somehow I still have algae. Can algae really grow with levels at 7PPM? I guess I just need to go higher. I never realized how stubborn algae can be.

 

[Mendy48]

With a CYA of 40, your FC should remain at 16. Maintaining it there at all times. If I'm reading this correctly, your FC (that you brought it up to) is at 11. It should be at a 16 with a CYA of 40. Maintain the SLAM level by adding the correct amount of chlorine when necessary. Make sure to reach your SLAM target level.

Make sure you leave you pump running 24/7 while SLAMing your pool (proper circulation/filtration of the pool water is recommended). Again, do your best to maintain the proper SLAM "FC" level based on your current CYA FC/CYA. Continue vacuuming and brushing (brush brush brush) your pool each day while in SLAM mood.

 

[A_kraker99]

I feel so defeated. This is the first time I have had to do this :-(

 

[Mendy48]

I feel so defeated. This is the first time I have had to do this :-(

Don't feel defeated. Just keep following the SLAM process and you'll be fine. Don't cut any corners, just follow it. I had to SLAM my pool some time ago and "boy" was it frustrating, but I kept on it and the results were outstanding. So don't give up.

 

[Danforth]

This will be easy! Just keep the FC at the shock level for your CYA and then maintain it until you pass the SLAM criteria. Brushing daily is important as well.

I have kept my pool at or above target FC levels for my CYA for months and just got a patch of algae on the pool floor a month or so ago. It was from getting lazy about brushing. Even at perfect chemistry levels, you can have areas of poor circulation where algae can accumulate. Brushing, or running a good pool robot regularly, mitigates that.