SLAM unsuccessful? Things not quite making sense...

[winchie]

We had gotten back from a trip over a week away where FC had drifted low and predictably grew a batch of algae. Ran a slam for about 5 days and seemed to work well. Water was crystal clear, CC was virtually undetectable or 0 consistently, minimal chlorine loss (didn't have time to run OCLT). Traveled again for a few days and returned to another growth of algae all over, FC was still at 8.0 and 0 CC. Going back to SLAM all over again, and will stick with it for the long haul this time. Curious if that seems odd that algae would grow at FC of 8 and also have no CC's. Probably need to do a better job brushing and scrubbing the pool during the slam, even when it looks like everything is clear. Levels that resulted in algae growth below:
Does any of the above make people think that it might be mustard algae since it is so hard to kill? Or just didn't give it enough time/scrubbing last time?
Any drawbacks to running somewhat above SLAM levels (20 instead of 15), to prevent dropping below SLAM levels and minimize number of times a day you have to test it?
My liquid chlorine additions (Walmart pool essentials liquid chlorine, 10%) seem to be shooting me higher than Pool Math app calculates. Is that a common thing? (Do have the app set to 10% liquid chlorine for calculations.) Shooting lower makes sense (chlorine break down in jugs over time), but higher seems odd unless they are actually a higher percentage than listed on bottles.

 

[Bperry]

We had gotten back from a trip over a week away where FC had drifted low and predictably grew a batch of algae. Ran a slam for about 5 days and seemed to work well. Water was crystal clear, CC was virtually undetectable or 0 consistently, minimal chlorine loss (didn't have time to run OCLT). Traveled again for a few days and returned to another growth of algae all over, FC was still at 8.0 and 0 CC. Going back to SLAM all over again, and will stick with it for the long haul this time. Curious if that seems odd that algae would grow at FC of 8 and also have no CC's. Probably need to do a better job brushing and scrubbing the pool during the slam, even when it looks like everything is clear. Levels that resulted in algae growth below:View attachment 602588
Does any of the above make people think that it might be mustard algae since it is so hard to kill? Or just didn't give it enough time/scrubbing last time?
Any drawbacks to running somewhat above SLAM levels (20 instead of 15), to prevent dropping below SLAM levels and minimize number of times a day you have to test it?
My liquid chlorine additions (Walmart pool essentials liquid chlorine, 10%) seem to be shooting me higher than Pool Math app calculates. Is that a common thing? (Do have the app set to 10% liquid chlorine for calculations.) Shooting lower makes sense (chlorine break down in jugs over time), but higher seems odd unless they are actually a higher percentage than listed on bottles.

Going higher than slam just wastes chlorine. If uou didnt so an OCLT originally then you didnt pass the first SLAM which is maybe why the bad stuff popped up again. Just follow the steps…

 

[setsailsoon]

Win,

Welcome to TFP! Vacations are difficult to deal with unless you have a fellow TFPer that can help. Your SLAM issue is because you probably just SLA'd. Not hard to fix just do a full SLAM as soon as you can. This means you need to be sure it's completed before you stop. You will shorten the SLAM if you can check the FC level every 3-4 hrs first day and bring it up to SLAM level. Going over wastes chlorine and can do damage so try not to do this. The longer you go without SLAMing when it's needed the more benefit you'll get from frequent FC checks first day or so of a SLAM.

I've found Pool Math extremely good at predicting FC levels. If that's not happening for you could be chlorine hasn't completely mixed and/or your pool volume is off. Not likely your LC is higher % but if it is that can cause this too.

I hope this is helpful.

Chris