Is this even algae?

[rdtsc]

Hello TFP, put in this pool last summer. So far this year the swimming's been great, but after these last weeks of very high temperatures (water got to 88), I seem to be having an algae issue... or some kind of precipitant issue?



pH 7.2
FC 15
CC 0
CH 150
TA 0
CYA 65

I have the frog "mineral" system, but have not been using it. I cut open several of the frog chlorine packs and fill them with trichlor tabs. The "mineral" thing is still in, never changed it and don't plan on it. Usually this "fancy chlorinator system" works well, but over the past few weeks, the chlorine level got quite high for no reason. Normally the pool can be run on low speed with a frog setting of "1" or less and chlorine stays constant around 2ppm. But for some reason the chlorine kept going up, so I set the frog to 0, and it still kept going up. It got over 19 and started looking hazy, so I took the frog chlorine pack out. Perhaps an o-ring failed.



An entire pack (a couple pounds worth) of trichlor was dissolved in just a few days. So that of course, raised the CYA significantly and lowered pH. Alkalinity is zero because the pH went down to 6.2, so I added soda ash to raise the pH, which burned off the TA. Then the greenish-brown sludge issue started. At first I thought it was mud from the kids, was somewhat stubborn to vacuum but I got it, cleaned the (dirty) filter, and thought things would be good. Put pump on high and it's been on high ever since.



The CYA was up to 85 and FC 15, the next morning the bottom had more patches of this greenish-brown sludge. Always in the dips and crevices. So I vacuumed/scrubbed it again (FC 15) and threw in a half gallon of 12% bleach. Much to my surprise, this actually made the issue worse! CC has stayed constant at 0, so it doesn't seem like anything is getting killed off. Vacuumed it again, next day, same thing.

So then I assumed that the CYA being so high must be locking up all the available chlorine, so I drained 4" or so and replaced with fresh water. CYA down to 60, but adding the rest of that gallon (FC 25) again did nothing (CC 0) and instead made the issue worse again.



At this point I'm grasping at straws. Was thinking perhaps it was a TDS/metal issue (possibly from the frog "mineral" thing), so I tried some metal-out, but it has had zero effect.

Any ideas would be very much appreciated. Is this even algae? Was going to fix the TA but no sense in doing that if I need to adjust the pH first.

 

[pooldv]

It sounds like algae. You can do an Overnight Chlorine Loss Test to see if there is something organic growing in the pool. If yes then SLAM Process to kill it.

 

[max2k]

I'd remove any chemical dispensers you might have left in there, run one set of tests to get a reference point (FC, CC, CYA, pH). Please note pH test produces incorrect results if FC is above 10 ppm, so just skip it if FC is higher.
Then I'd try to measure overnight FC loss as part of OCLT already recommended and post all that here.

Is your pump/filter in good working order?

If you eventually decide to SLAM please remember it's a multi- day process, not a single event so it is essential to be able to do regular tests and FC adjustments along its course.

 

[rdtsc]

Good news. I slammed it (more) last night, raising FC to 35. Sheesh I think that's high, but this morning there was the distinctive odor of CC's finally and 10ppm chlorine was lost overnight. Still some sludge, but vacuumed it then brought FC back up to 35. The water has lost it's greenish tinge. It's still cloudy, but looking better!



Filter works *well, new it showed 9psi, cleaned it shows 10psi, clogged at 14. Still running on high, 10psi, good flow. *Discovered the pump must be sucking in air somewhere when on high. The canister slowly fills up with air over the course of several hours, lowering the effective filter area. Doesn't do this on low.

OK so it is algae, and two things lead up to this problem:
1. "Frog" system did not dispense chlorine reliably, resulting in overuse of trichlor --> excessive CYA --> no FC --> muck.
2. Pump cavitating or sucking air into canister, reducing surface area = little effective filtration.

Uggh. Trichlor is so convenient; a pail lasts a whole season with minimal fiddling. But this CYA is a problem.

 

[Texas Splash]

Many locations up north can squeak-by with tablet use because of the shorter swim season .... as long as the starting CYA that season wasn't already high. Unfortunately yours shot-up quickly from that tri-chlor pack that was used. Once you get that CYA where you want it, at least it won't climb again unless you really want it to. Hopefully the prior use of the Frog system didn't add too much metal to the water either. If you ever find yourself doing a partial water exchange to lower CYA, it should help to lower the metals content as well.

 

[rdtsc]

Thanks for all the help. Water is crystal-clear again, although had to maintain a 35-ish FC for more than a few days. Found that a bag of river rocks used to weight the steps was loaded with algae. Went through about five bottles of 12% bleach. Even when "off" the Frog kept delivering trichlor, so I removed it. The CYA continued to rise long after this; right now it's around 115, so keeping FC around 13. CYA is very insidious stuff! On a plus note, the FC doesn't degrade much due to sunlight anymore. Switching over to 12% bleach for the rest of the season.