I think I have algae

[Brad_C]

Details in sig, but fibreglass pool, sand filter, single speed pump and SWG that can make 1.2ppm/hr (itty bitty pool)

CYA - 70
Salt - 4600
CH - 260
TA - 100
pH - 7.8
Borates - 55
CC - 0
FC - 20

The FC is high because the kids left the filter on and at 1.2ppm/hr it gets up fast. Because I've not been present reliably I've set it up so the FC never drops below 10. Daily tests at worst-case time (sunset on a hot day with no filtering during daylight hours) confirm this.

The pool passes the OCLT. The water is crystal clear but goes a little bit cloudy after swiming and requires an extra couple of hours filtering to clear back up. Filter pressure is rising.
It has all the hallmarks of Algae, but it's not really consuming chlorine and the FC level has never dropped below 10.

I know it's not right as last summer I never had to backwash the filter and it never clouded up.

I tried a SLAM in October and it ticked all the boxes after a single day, so I let it run for 3 days just to be sure.

Now, I topped up the salt, borates & CYA a couple of months ago (winter rain washout). Salt and borates pre-SLAM and CYA post. I haven't added acid since Feb and I've only used 12% liquid chlorine for the SLAM. Our water temp never drops to where the SWG isn't effective, so it kinda maintains itself most of the year. pH likes to sit between 7.4 & 7.8 but our tap water has a TA of > 110 so it does creep up over summer and require the odd adjustment.

No sign of green anywhere (it usually pops up on the wall in the shade if it's coming). So I'm a bit baffled. The rising filter pressure tells me something is wrong, but I would have though the cloudy after a swim would point to algae. But at an FC of 20ppm?

 

[mknauss]

Do an Overnight Chlorine Loss Test

Other item is your pH test is invalid with a FC above 10 ppm.

Any potions of any kind added lately?

 

[ajw22]

How old are your CCL test reagents?

 

[Brad_C]

My ph test is fine, I use a meter that is properly managed and calibrated. The CH and TA reagents are a year old, the chlorine and CYA are 6 months. Chlorine level measurement correlates well to theoretical additions by liquid or SWG.

I don't do "potions". Chemical addition in the last 12 months have been Salt, calcium chloride, boric acid a couple of months ago to bring post winter levels back up, CYA a week or so after that in 2 doses. Some Hydrochloric Acid back in Feb and some ~12% sodium hypochlorite for the SLAM process.

I did say in the first post it passes the OCLT and has done every time I've tried it.

 

[Brad_C]

Right, I think I've defeated it.

I backwashed the filter on Saturday, brought the FC level up to >28, switched off the SWG and let it ride. The continous filtering cleared the water right up in a matter of hours, but immediately people jumped in the pool it went cloudy again. It was still passing the OCLT.
We've had serious sunshine, so it has been burning up the FC during the day and probably to account for the swimmers, so kept topping it back up to ~30ppm twice a day. This has repeated for 4 days, but today after a swim it has remained clear.

Oddly enough, not a trace of green and it never used chlorine overnight, but there was obviously still something there which was triggered by swimmer byproducts.

Since I have plenty of 12.5% left over I might leave it elevated for another day or so as it'll get a hammering tomorrow, but whatever was there appears to have been defeated.

As an aside, I lowered the pH to ~7.5 before I started and bringing the FC up to 30 pushed it up to about 7.75. Last year, pre-borates when I did that it pushed well over 8, so the buffering effect is quite pronounced.

 

[AUSpool]

Most of the eastern seaboard of Australia is still on fire, our cities have had a lot of days with very poor air quality and all this ends up in the pool. I’ve been a preoccupied but I think Perth has had some fires to? This potentially is what you have, very fine particulate matter that will go through the filter when it’s clean. It settles to the bottom overnight and is mostly inorganic in nature and wont interact with free chlorine but as soon as swimmers jump in it is stirred up again.

If your comfortable with high chlorine at higher CYA, I would keep it between 6 & 10ppm.

 

[Brad_C]

Yeah, we've been pretty lucky actually. We had one fire a few years ago where there was the finest dusting of ash on stuff outside, but we've pretty much had nothing local this season or the last couple. The ones we've had here have been either North of the city and moving North, or South and moving South/East. We can see the smoke but it's always blowing away from us.

The East coast has certainly copped it this year though.

 

[Brad_C]

So, the algae is back and I've found the source. Actually, it never left.

My fibreglass pool shell is 50 years old this year. There are a number of areas where the gelcoat is compromised, and right at the deep end it's pretty much worn back to the glass. This leaves a heavily textured fibreglass finish that I can't effectively clean with the broom. I have managed to scrub most of it out using a tiny nail brush, but there are pores in the glass where I can physically see the algae and can't attack it mechanically because the pore size is much smaller than the diameter of the bristle.

Since I have algae and it's time for SLAM, I've tried another approach. I removed everything from the pool (toys, cleaner, debris) and left it to stand for an hour until I was sure the water was as still as it was going to get. I then used a 6 ft length of 20mm PVC pipe and a funnel to pour 4L of 12.5% directly over the algae while very slowly moving along the end of the pool to get as much coverage as I can.

That seemed to have knocked off most of it. I can still see some tucked up in the "dark corner". The one that gets the least day light. That is where the algae seems to pop up first.
So when I next do a chlorine addition I'll do it there.

That was one way of doing it. I was also thinking maybe of a pile of cal-hypo in a sock strapped to the end of the pole to rub over the affected surfaces directly.

So, I'm soliciting input on ideas of how to effectively get the algae when I can't physically scrub it out *and* given it's a dark place that likes algae and can't be mechanically cleaned how I might stop it taking hold again. Has anyone used a high pressure washer under water?

This algae quite happily survived 4 days of ~35ppm chlorine (SLAM level 24), so it seems to really requires a serious punch to kill it off.

 

[kimkats]

WOW what a story this is! You sure have done some good detective work as well! So I am going to throw a couple ideas up and see what sticks:

-Funnel with a hose that leads to a plumber plunger with the hopes the plunger will kind of "stick" to the area the algae is in the pour the chlorine and let it sit on the area. The down side of that is will the chlorine do harm to the pool shell?

-Towel soaked in chlorine then put on some flat (not sure what yet) and held against the spot some how.

Any chance of of redoing the gel cover? (not even sure if this can be done so.......)

Kim

 

[Katodude]

I dont know if this is a good idea for fiberglass or not, but I used to use a pressure washer in the pool to remove spots of black algae years ago. If you are down to the glass you might create more damage.

 

[Brad_C]

-Funnel with a hose that leads to a plumber plunger with the hopes the plunger will kind of "stick" to the area the algae is in the pour the chlorine and let it sit on the area. The down side of that is will the chlorine do harm to the pool shell?

I gave that a try. Didn't touch it. Great idea though.

I dont know if this is a good idea for fiberglass or not, but I used to use a pressure washer in the pool to remove spots of black algae years ago. If you are down to the glass you might create more damage.

The high pressure washer didn't touch it. I wasn't game to go any closer and risk more damage to the glass, but I did go close enough to "feather" the edge of the existing gel coat, so I can't see how any biofilm could withstand that.

Given the remainder of the algae in that area disappeared literally before my eyes as I poured liquid chlorine in its immediate vicinity, and a pool of liquid chlorine, nor high pressure washer touched this stuff I'm beginning to think it's some form of stain in the epoxy. Having a look at some web pages about organic tannin stains it's probably not too far from the mark but having been there for who knows how long it just doesn't want to shift.

Its location is right under a Bottlebrush tree (which are known for leaving stains) so I'm tempted just to leave it alone. I now know the liquid chlorine / pipe / funnel trick will get the remainder of the algae that the brush and pool cleaner won't touch. I might just have to resign myself to a periodic dump of liquid into that area. I have some old socks and some cal-hypo, so I might try that and let it sit for a while before giving up entirely. Seeing as the liquid didn't touch it I'm not holding out much hope, but I have the stuff so it's a no-cost attempt.