SLAM process for mustard algae

[Sandylea]

Hello! It’s my first time posting here. Pool is a little over a year old , plaster, 17k gallons, cartridge filter, variable speed pump, and this is my first attempt at a SLAM

I have noticed some mustard algae growth on the walls of the shady sides of my pool. I am able to brush it off, but it returns within a couple of days. I started the SLAM process on Monday morning (8/8). I have dumped about 20 gallons of liquid chlorine (12.5%) in over the past 60 hours, brushed daily, ran vacuum (Dolphin M400) 3 times daily for the past 3 days, pump has been on the entire time.

CYA 70 (I know this is high, but I will wait until we aren’t in a drought to partially drain my pool)

CC has always been .5 or zero

Water is (and always has been) crystal clear

I am having trouble getting my FC above 25. I have been adding chlorine every 3-4 hours and it just keeps staying around 25. Pool gets full sun for about 5 hours and it has been 100 degrees (but it did rain yesterday and today). I did get the FC up to 29 yesterday, but a few hours later it went down to 25. Could my cartridge filter (possibly dirty- haven’t checked, but will tomorrow) be eating away at my chlorine? Is there a point where the FC won’t rise/ stay any higher than a certain point (25 in my case)? I did let the FC get to zero at one point (shortly before I noticed the algae growth). Just wondering if this is an absurd amount of chlorine to be adding to a very clean looking pool?
Thank you! This forum is SO helpful!

 

[Texas Splash]

Welcome to TFP! Your filter is not the issue, nor is the CYA of 70. Clear water can be misleading sometimes, and if the FC is falling it's due to one of two things - lack of CYA and/or algae. The fact your pool only receives sun for about 5 hours is even more reason to suspect algae. Have you done an Overnight Chlorine Loss Test? Have you removed the light if there is a niche and/or checked under the main drain covers if installed?

Pool Care Basics

 

[Sandylea]

Thank you! Under the 2 skimmer baskets, there was a coating of dark brown/ black scum. I cleaned that up, and I am hopeful that my FC holds tonight! . If not, I will try removing the lights and main drain cover. My husband removed the drain cover at the bottom of the connected spa, and it was clean. I hope that means the main drain in the deep end (same shaded side of the pool as the spa) is also clean. It would be a major pain to swim down there and unscrew the screws to remove it. Hoping it doesn’t come to that! Thanks again!!

 

[Sandylea]

Welcome to TFP! Your filter is not the issue, nor is the CYA of 70. Clear water can be misleading sometimes, and if the FC is falling it's due to one of two things - lack of CYA and/or algae. The fact your pool only receives sun for about 5 hours is even more reason to suspect algae. Have you done an Overnight Chlorine Loss Test? Have you removed the light if there is a niche and/or checked under the main drain covers if installed?

Pool Care BasicsPool Care Basics

Pool Care Basics

 

[Sandylea]

Pool Care Basics

Thank you so much for this great advice! After cleaning the brown scum off of the skimmer wells yesterday, I was disappointed that I didn’t pass the overnight FC test and the pool was still using chlorine way too fast (1 gallon added and 3 hours later FC was the same at 25). Taking your advice, my husband swam down into the deep end and removed the faceplate on the two drains (that was fun ), and the other drain in the spa. All 3 were dirty with the same brownish scum (same thing that was in the skimmers). He cleaned all of those out as best as he could, and they look much better. After he did this, I turned the pump back on, brushed, ran the vacuum and added 1 more gallon of chlorine. FC was at 25 before I added the last gallon and it only went up to 27, 4 hours later (with no sun).

Now that we have cleaned every possible crevice (lights are small LED “nicheless” lights, so I don’t think algae could grown behind them? ), should I assume that the FC didn’t rise as much as “pool math” said it would because it was consumed by the algae in the water that we just brushed off?

Also, should I check my PH during this process at all? I’m sure with the gallons of chlorine I have added (I’ve lost count), my pH is probably not so great.

I added another gallon of chlorine for the night and I am hoping and praying it will not be gone tomorrow. Tomorrow will be day 6 of the SLAM and I am ready to be done with this! Tomorrow I will head out to buy the rest of the liquid chlorine in the DFW metroplex. Thanks again for all your help!!

 

[Texas Splash]

Good catch in the drain areas. No need to worry about LED lights. No need to worry about the pH until you have completed the SLAM Process by passing all 3 SLAM criteria. Hang in there, you may be getting close now that you exposed all that brown junk. At some point, you might confirm your CYA again just to ensure you are maintaining the proper FC SLAM level. Other than that, stick with it as best as you can. Once it's all done you'll be glad you did.