Mustard algae or filter issue?

Rangeball

Well-known member
May 25, 2007
785
#1
My dad's AG pool has me scratching my head. 24' round by 4.5' deep, 15,200 gal. Hayward 1hp pump and older pentair 50 gpm DE bump filter.

We opened it late and there was a good bit of algae on the floor and walls. Shocked it, he didn't want to vacuum to waste (on a sand point) so he went through several filter changes, and eventually bought a dolphin robo-kleen which actually does a nice job.

Anyway, pool is clear and water sparkles. He's maintaining an adequate FC level for his CYA and there is no CC. However, every morning, the floor of the pool is dirtied with a fine brownish gray dust. There are lots of trees around, but nothing seems to be pollinating. The ability to hold a FC residual and lack of CCs leads me to doubt its "mustard" algae, especially since it shows back up to the level it does overnight.

I don't know how to calculate the head for AG pumps, but his flow is tremendous. I suspect he's exceeding his filter's max, but don't know for sure. We recently replaced his pressure gauge, and it's been reading fine, but when the flow visibly diminishes (when he was vacuuming), the pressure isn't going up much like it did in the past. So I'm left wondering if possibly he has a tear in his filter grid that is letting sediment through and back into the pool.

I plan to have him turn his pump off overnight (he'd been running non-stop while we got things going) to test the filter. If there is less deposited on the pool the next morning, it would point to a filter problem, right?

Thoughts?
 

tagprod

LifeTime Supporter
Jul 3, 2007
489
Tomball, Texas
#2
I've had mustard algae in the past so I definitely know how to identify it when I see it. I've noticed that in the early stages of Mustard algae my water looks great and no CC's are showing up in my tests. I'm usually pretty good about brushing once or twice a week and I think that retards the growth. It seems to be a rather slow growing Algae that doesn't throw your pool chemistry totally out of whack. To really get rif of it, a vigilant attack of chlorine, brushing and filtering will get rid of it. Most of the time, you just trust your numbers (and I do) but like I said, the early stages of mustard algae don't show up as CC's - at least not in my pool. Are the areas in the shade where you see the mustard algae?
 

Rangeball

Well-known member
May 25, 2007
785
#3
I'm not yet convinced it's mustard algae. It's spread over the entire pool floor, not totally covered, but kind of splotchy, like deposits of sand or something. The pool floor can be totally clean at night after a few vacuum cycles, but then covered again the next morning. I wouldn't think algae could grow that fast (9-10 hours).

I think it's the filter.
 

Rangeball

Well-known member
May 25, 2007
785
#5
That's comforting :) Like I said, I'm grasping at straws, and this is the only thing that makes any sense, although his water is crystal clear, as is his return flow.

He's going to turn the pump off tonight after the floor is clear and the bleach is circulated. I'll post an update.
 

waste

TFP Expert
LifeTime Supporter
Mar 29, 2007
4,160
Coastalish 'down easter'
#6
Rangeball said:
That's comforting :) Like I said, I'm grasping at straws, and this is the only thing that makes any sense, although his water is crystal clear, as is his return flow.

He's going to turn the pump off tonight after the floor is clear and the bleach is circulated. I'll post an update.
Thank you , please do that. It certainly sounds like 'blow-by' from the filter - this will confirm that :goodjob:
 

Rangeball

Well-known member
May 25, 2007
785
#7
Well, you can lead a horse to water...

He didn't turn the pump off. When he got home the floor was clear, so he just left it alone :( There is a possibility that his robo-kleen is causing the problem. He had a lot of stuff on the floor, and the robo moves pretty fast, stirring some of it up. It could just be stuff settling down when the vac stops, which would explain the diminishing re-deposits each morning.

He said this morning there was less deposits, and he seems happy.

Oh well, it's his pool. I'll quite worrying about it until he asks again.

Thanks all.