Dead Algae on the bottom every day

[iamnos]

Pool is ~3 months old, had a bit of a bloom a few weeks in, but did a SLAM and came out great on the other side. Over the last couple of weeks I'd say, we've been getting dead algae on the bottom every day. FC loss in a ~24 hour period is generally between 1.0 and 2.0. One day it was almost 3, but that was after being uncovered longer that day, and more swim time that is normal, so not totally unexpected. The lowest FC got was 3.5.

FC 6.5 (I aim for 6.5 - 7.0)
CC 0 (sometimes a very slight pink tinge, but hardly noticeable)
pH 7.4
CYA 40
TA 110
CH 130

The water is always sparkling and clear, but every day, in a few areas of low circulation, there's always this green/brown powder on the bottom. I've started vacuuming daily and brushing the walls about every other day. I did a backwash and rinse yesterday, even though we were only up about 1 PSI from normal (about 16).

Should I run another SLAM?

 

[borjis]

I did a slam once and I only saw the dead algae clumps on the floor near the very end of it.

I would do an overnight chlorine loss test for 3 days in a row first. Then go from there.

 

[iamnos]

Well, first night was good. 0.5 (although, it might have been less). I didn't have great lighting out by the pool last night. Tonight I'll bring the sample inside to better lighting.

 

[Oly]

Not sure what "a bit of a bloom" means exactly but realize you have areas in your pool where algae can hole up and be impossible to see. Light niche (area behind the light) and auto fill piping are two areas that can harbor algae.

 

[iamnos]

I had some algae, very slightly cloudy water in the deep end. I realize there are areas that are more likely where algae can "hide", but shouldn't the FC and pump running take care of those areas?

 

[frogabog]

I had some algae, very slightly cloudy water in the deep end. I realize there are areas that are more likely where algae can "hide", but shouldn't the FC and pump running take care of those areas?

Are you brushing multiple times a day? Normally yes, the pump and FC should handle even the low flow areas. But when you're dealing with an algae bloom any pool needs brushing and disturbing of the algae areas so that the FC can actually get to doing it's main job on the algae, where under normal circumstances FC doesn't need to attack so hard without algae.

 

[Oly]

Does your pool have an auto fill system?
Have you taken a look behind your light?

 

[iamnos]

It does not have an auto fill, I've scrubbed the walls, including around all fixtures like the lights, drains, skimmer, returns, etc.

 

[iamnos]

Are you brushing multiple times a day? Normally yes, the pump and FC should handle even the low flow areas. But when you're dealing with an algae bloom any pool needs brushing and disturbing of the algae areas so that the FC can actually get to doing it's main job on the algae, where under normal circumstances FC doesn't need to attack so hard without algae.

I haven't been doing this multiple times a day. I'll start tomorrow (just closed everything up for the night). 24 hour chlorine loss was 2.0ppm being open most of the day and more than average swim time, so it's not using much.

 

[Oly]

You are right 2ppm FC loss in 24 hrs is low.
Stay the course and see if things improve.

 

[iamnos]

Okay, updating an old post. Things have continued with the same. Overnight loss has been 0.5ppm (or less) every time I checked, which was about 3 or 4 nights in a row.

Most recently, we were out of town for a total of about 80 hours. Just before we left, I boosted the FC to about 10.5 As soon as we got back, I checked, and it was at 6.5. Today, opened it up, and lots of the same on the bottom. I'd been vacuuming and scrubbing walls every day. I should have taken a picture before I did that, but I didn't think about it until after. The water is VERY clear. Seeing down into the deep end (~6.5') is perfectly clear, Just the sediment on the bottom.

I noticed some of whatever this is around the returns, so with the pump off I took out the ends and attached pictures of them, hopefully can help the experts figure out what's happening here. The brown staining wipes away with a bit of force with my thumb and it appears on both returns.



Numbers today:
CC: 0
FC: 5.0
pH 7.4
CYA 40
TA 100
CH 130

edit:
Likely unrelated, but I did notice that we have a small leak in the plumbing (above ground) between the filter and heater. I have the pump currently running from 8:30am to 5:30pm, and in that time we might lose a cup or so of water. The pipe is slightly above the concrete pad the equipment sits on, so it shouldn't be sucking in anything, other than maybe some air.

 

[iamnos]

Is it possible this is pollen or is it more likely to be mustard algae?

Picture of the pool about 24 hours after a full vacuum and only about 1.0FC loss.

And another after I collected some from the bottom in a small measuring cup

 

[JJ_Tex]

Your chlorine is too low if you are seeing algae and trying to SLAM. The FC should be 16 for a CYA of 40, and you are at 5.0. Once you are done with the SLAM, your normal range should be 5-7.

The Free Chlorine and Cyanuric Acid Relationship

Managing your cyanuric acid and Free Chlorine levels is key to stabilizing your pool. Learn how these two items affect each other.

www.troublefreepool.com

 

[iamnos]

I'm not trying to SLAM at the moment, I'm trying to ask if I should. My chlorine usage seems too low to suggest algae, and the water is clear, but I have this sediment on the bottom every day

 

[frogabog]

How long ago was your last OCLT? Last week's OCLT doesn't equate OCLT results for today. You could do another tonight, or just SLAM because that is not normal...

Whatever the case, that looks like something slimy which then lends itself to algae. I'd say raise FC to SLAM level, test an hour later and see how much FC you lose.

Mustard algae tends to form in the shadows, if you don't have that stuff in the shadows it's probably just regular algae. Pollen is usually associated with blooms in the spring, not late summer.

 

[iamnos]

I've never seen an OCLT more than 0.5. last one was two nights ago, and several times throughout the last few weeks that this has been going on. The pool hasn't gotten a lot of use lately so the solar cover has been on most of the time, so the entire pool is "shaded".

Just double checked and levels are all good, though CYA is 30 now. It has been probably 3 weeks since I tested it.

Starting a SLAM again now.

 

[frogabog]

Sounds like a plan! Might want to test at 30 minutes to see what the FC level is, then test an hour later to check for loss. Make sure to brush all that stuff up into suspension. Let us know what your test results are.

 

[iamnos]

Did a full vac of the bottom and walls, then added enough chlorine to bring it up to 12. ~45 minutes later it was between 11.5 and 12. I'm betting that was just the difference between what it actually needed to get to 12 and what I actually added (still trying to figure out the exact volume of this pool). I'll check it again in a couple hours and bring it up to at least 12.

 

[frogabog]

Testing 30-45 minutes after adding is a great way to get your pool volume sorted. Sounds like you're really close already!

If the sun is off the pool now, a test in the next 2-4 hours should tell you something about that stuff you're seeing.

 

[iamnos]

Well, almost 5 days in and things have vastly improved. Virtually nothing on the bottom yesterday when I vacuumed. OCLT was 0.5ppm, though it's never gone above 1.0. The deep end (~6.5') looks clear looking straight down, but looking from the shallow end maybe just a bit cloudy. Going to SLAM for another day or two anyways. But doing the SLAM has definitely helped a lot.