SLAM for a week, and cc increasing

[gardenlady]

I have slammed before, with great results, but I'm having trouble this time. The water cleared to look great after 4 days, the pool almost passed OCLT, cc was 1.0. Pool still looks great, but OCLT is still too high, and cc is now 2.0! I neglected to check the pH before I started, could this be the problem? PH had generally been good this year, but it does tend to rise here. After adding 21 gallons of 10% Bleach, I'm thinking pH may be the problem. What do you think?

32K gallon in-ground old plaster pool with sand filter. CYA is 60, I've been trying to maintain FC at 24 using 10% bleach (and some chlorine is added during the day with a tablet feeder for convenience when I can't be at home.) The water temp is around 90; using the solar cover during the day to reduce solar destruction of Cl and evaporation. I live in Texas, and our highs are around 100º.

 

[Teald024]

No, it's not the pH. It is likely the solar cover. By leaving the solar cover on, the sun can't break down the CC and allow them to escape. You should pull off the cover for a few hours in the evening (or any time while the suns out) to let the pool breath. Try this to see if that helps.

 

[gardenlady]

Thanks for your quick reply. I'm trying your advice. Without the cover the cc was down to 1.5 this morning. The cover has been off all day, and the cc is still 1.5 and I can smell it a little. I'm not adding any bleach, but the feeder is on. FC has gone down to upper teens, and seems to be holding with just the feeder. I plan to let the Chlorine Level go down to 7-9 now, and see what happens with the cover off, unless you recommend bringing it back to slam level. Water is crystal clear.

 

[Teald024]

I would recommend keeping FC at SLAM level until the CC are down to 0.5ppm or less. Use the liquid chlorine as your FC source.

Keep in mind that as you use those trichlor tabs, they are adding CYA to your water. You will need to maintain FC per the FC/CYA Levels. You will need to increase FC to compensate for your rising CYA levels. Each 7oz (3") puck will only raise your FC by 1.5 and will raise CYA by 0.9ppm. It may not seem much per puck, but it really adds up over time.

 

[gardenlady]

Thank you. Will do. I'll try to just use the pucks for vacation. I'll let you know the outcome on the cc.

 

[gardenlady]

Here is my report. After a total of 2 weeks, the SLAM was complete. I think removing the cover helped a little, but it was strange because my cc seemed to vary from just over .5 to 2.0 during the last few days of the SLAM.
Is it possible that there was some black algae lurking and causing the cc problem? After the SLAM, I accidentally let Cl drop to 6, and within a day had a small amount of black algae pop up! It responded to treatment within a few days.