Could my waterfall basins be the cause of my recurring algae issue?

gkw4815

Well-known member
Aug 31, 2021
264
Memorial Villages, TX
Pool Size
25000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pureline Crystal Pure 60,000
Am entering my fourth season with our pool (third season during which I've maintained the pool myself).

Despite (mostly) following TFP practices and testing my water several times a week, I tend to struggle with algae growth whenever my water temps are in the upper 70s or higher. Last season, I was able to mostly keep algae at bay with weekly brushing and monthly treatments of Chlorox Pool & Spa Algaecide % Clarifier, which would reliably clear up the pool overnight with a single one-gallon application.

My pool gets partial sun and is surrounded by lots of vegetation. I do cover it from early November through early February, which keeps it mostly leaf-free. I believe the plaster is original to the 29-year-old pool. It looks very presentable but is of course rougher than newer plaster would be. I don't believe this should matter as long as chlorine levels are sufficiently high, but probably makes regular brushing more important than it would otherwise be.

This season I'd really like to get to the bottom of the issue and wean off the algaecide treatments. I'm currently partway through a SLAM (passed OCLT but still at 1ppm CCs).

One oddity of the pool is that the right and left natural stone waterfalls were built very differently, almost like they were built by different crews or one crew who was learning as they went. The left waterfall is designed so that it traps almost no water. After the waterfalls are switched off, any water will drain down into the pool within an hour or less. However, the right waterfall has multiple deep basins that can trap water for days or more before it fully evaporates. These basins tend to get pretty grungy as shown in the photo - I cleaned them last year just before covering the pool and they're already nasty again.

I run the waterfalls for 5 minutes daily and sometimes for 30+ minutes. In consideration of their condition - would this likely be enough to contribute to algae growth / elevated chlorine demand in the pool as a whole?

I'm going to try leaving the waterfalls off for a few weeks and see if that makes any difference - but am curious if this behavior is a common issue with "basin-type" water features..
 

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Waterfalls? ... maybe. One thing's for sure, you MUST follow the SLAM Process to the letter. No shortcuts. During this time, with the FC properly maintained at SLAM level, you must scrub those basins. Every inch of that pool or anything that touches water much be scrubbed for chlorine to penetrate it.

After the SLAM, no more snake oils. Algaecides, etc, nope. A proper FC level, based on the current CYA, is the key.

If you have any questions let us know.
 
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The still water sitting in the basins are likely breeding algae and then dumping it into your pool when you run the waterfall. We have seen this before with water features that hold puddles of water.

Any chlorine in the puddles of water likely cannot survive a full day in the Texas sun. Then the FC drops low enough for algae to survive in the puddles.
 
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Thank you ajw22, that's what I'd figured.

The right fix is probably to rebuild the waterfall and/or "shallow" the basins so they can't hold water, but that sounds pretty involved. Maybe will do so when we replaster the whole pool in ~5 years or so.

In the meantime, I'll thoroughly clean the basins and check into drilling small drain holes that would drain standing water from them into the pool.
 
5 and 50, although I admit I haven't been testing and adjusting as often as I should (before the SLAM - 1-2x weekly, but currently 2-3x a day).
Run a lot hotter.

In TX you need CYA of 70-80 and keep your FC around 9.
 
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At 50 CYA and a FC of 5, you are below the target range (6-8). Your pool is telling you it needs more chlorine, listen to it.

Below is a chart I put together to help visualize the target ranges. When adding chlorine, I would target 8-10 and let it drift down to the target range. If you still get algae after that, then listen to your pool and dose to 10-12. You have a long way to go before your FC levels are considered high, and you already know what happens when they get low.

1744856633350.png
 
5 and 50, although I admit I haven't been testing and adjusting as often as I should
Ok. We're old friends so take it as a compliment I'm not sugar coating none of this. :hug:

But what. The actual. Flocc ?

Slacking is one thing, but instead of adding the chlorine and testing you know you're short on, you turn to algecide, clarifier and modifying the stone on your waterfall ?

If any of that worked would we be teaching everybody how we do, or teaching that ?

Algae = chlorine dipped to low, there are no two ways about it. Some folks have stubborn strains like mustard/black and they need even more than what works for most people, but once the appropriate levels are kept, *poof*. Err. No poof ??

SWGs sink alot of folks also as they don't consider *when* they produce FC in regards to the daily loss, nor when they test in regards to the daily loss. The 2 whens are just as important as the what of the test result. OK it's a 5. But if you're testing 5 in the AM and run overnight, you're losing 4 ppm today like a LC pool. Or 24/7 operation will lose a little less but still not come close to matching the mid day burnoff. If running 6 hours at 100% mid day, well then maybe the 5 FC was ok in the morning.

Then a system hiccup or false low salt reading during/after a big storm shuts the cell off for 12 hours and you have yourself a full FC swing pool with insane Texas UV.

The closer you run to min, the more you have to pay attention. I have a 2 day buffer at all times and if I see the green lights from the patio, I know I'm producing today and likely still have a 2 day buffer. I'll adjust a handful of times over the season but I'm fooling around at high target or above which allows me lots of slacking.
 
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