Recurring Green Algae after Slamming and Passing OCLT

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andrewdunne

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Jul 13, 2014
6
Austin, TX
I'm looking for some input as to why algae keeps reappearing after Slamming and successfully completing OCLT. This has happened twice now and I'm puzzled why this is happening. Thanks to this forum I had an algae free season all last year and want to have a repeat this year. After performing the SLAMMING and OCLT the FC has constantly been in the range of 3-7 ppm and CC is 0.5 ppm or less. The water is crystal clear but green areas keep appearing on the floor and benches after about a week of completing the SLAMMING process and OCLT.

Chemical Levels as of this morning are:

Calcium Hardness: 225 ppm
CYA:30
Total Alklinity(60-120): 75 ppm
PH: 7.4
FC: 5.5 ppm
CC: 0.5 ppm

I have a UV light that I thought maybe driving down the CC and giving me a false positive on the OCLT. However, I disconnected it on Sunday (6/21) of this week and I have not seen an increase in the CC over the last 5 days. I have not SLAMMED the pool since disconnecting the UV light because I wanted to see if the CC would increase without the presence of the UV light. Any input or ideas is much appreciated.
 
Well, it has begun to get hotter in our area, and today is no exception. :sun: While your FC appears to be 5.5 right now, you confirmed it has fluctuated from 3-7 - with an FC of 2 being your absolute minimum. In this intense heat, if that FC every did get to 2 ppm, that could've spurred an algae event right there. In addition, you might want to consider raising your CYA a bit to protect that FC based on the intense heat/sun in our area. I was at 30 and going through too much chlorine, so I bumped it up. Then after all the rain we had, and pool drainage, I lost some CYA and had to add back again. So while your numbers above generally look solid compared to the Recommend Levels chart, you might want to keep that FC steady at a slightly higher rate, and consider increasing CYA (perhaps to 40) to see if that helps.

Also make sure you have good circulation in the pool, and nothing in the pool that could be a home for organic material that hasn't already been cleaned & scrubbed (i.e. light fixtures, ladders, etc). Hope this helps.
 
Thanks for the feedback. Just a clarification, when you say fixtures, I'm assuming you mean anything that comes in contact with the water? If that is the case then that very well is part of the answer. I did have some algae on the stone that I removed just a couple of days ago. I guess I assumed that because the FC was high enough it would not matter if the algae on the stone came in contact with the water. Good to know. I guess I need to get rid of any visible algae before slamming again?

I was thinking about raising my CYA to 40 but was hesitant though because I'm using the Tabs.

Do you know if the UV does in fact lowers the CC?

Thanks for your help and suggestions.
 
Tabs certainly will begin to raise your CYA, but based on your FC consumption perhaps not fast enough for your needs. Certainly your option on waiting it out or adding some now. You probably know how TFP feels about using pucks on a routine basis. :) I'm not a UV expert, but my searches showed that yes UV does tend to lower CC. And you are correct about anything that comes in contact with the water could contribute to algae. I don't have a rock-type water feature, but perhaps someone else reading who has experience with one can give you more pointers on preventative maintenance. Enjoy your weekend!
 
If you have visible algae now, you need to SLAM before you raise your CYA.

What you are describing of algae growing on rocks in contact with the water or water fall areas is a problem with more "natural" looking pools. Anywhere water can puddle without flowing chlorinated water is a breeding ground for algae. Then, when it gets washed back in the pool you are off to the races again. That style of pool is beautiful, but more difficult to keep algae free.

UV is what normally lowers CC. That is why many indoor pools have supplemental UV systems.
 
I guess the good news is that the water doesn't puddle. I have a rock wall on the back of the pool that comes in contact with the pool water. Algae tends to form over time.

- - - Updated - - -

I have passed OCLT multiple times but I had the UV operational. I too thought it may be pollen given my FC has remained above 2 since I last SLAMMed it and passed the OCLT.

Since I shut off the UV 5 days ago wouldn't the CC accumulate over this period and be higher than 0.5? This was my reading this morning when I checked it.
 
I would get a spray bottle and put some bleach (50/50 bleach/water) in it and have a brush that is safe for you stone. Brush, spray, rinse, brush, spray, rinse, repeat as needed. THEN SLAM for 2 or 3 days to get rid of what ended up in the pool.

See if that helps!

Kim
 
andrewdunne said:
I guess the good news is that the water doesn't puddle. I have a rock wall on the back of the pool that comes in contact with the pool water. Algae tends to form over time.

- - - Updated - - -

I have passed OCLT multiple times but I had the UV operational. I too thought it may be pollen given my FC has remained above 2 since I last SLAMMed it and passed the OCLT.

Since I shut off the UV 5 days ago wouldn't the CC accumulate over this period and be higher than 0.5? This was my reading this morning when I checked it.
Click to expand...


if your pool is running and in sunlight, CC burns off pretty quick. I have never measured CC in my pool, even during a SLAM
 
Dan has it. The sun will burn off the CC fairly quickly which is one of the reasons supplemental UV is not recommended for outdoor residential pools by TFP. They just add to your chlorine demand.
 

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