Algaecide wanted?

[Brad_C]

G'day all,

I have an *old* fibreglass shell. There are considerable portions where the gelcoat is gone and we're down to the glass. The texture of the glass is such that Algae can hide in the texture and it's out of reach of brush bristles. This means no matter what chlorine level I put into the pool, I can't break the skin of the embedded algae for the chlorine to kill it.

Now, when we're at home and I brush the pool a couple of times a week, any accessible Algae sweeps up and the normal chlorine levels kill it. If however I go away for a week or so (like over the Christmas holidays) then I come back to a green film over the bottom of the pool which requires a couple of days elevated Chlorine levels, filtering and sweeping to get back to clear.

Don't tell me to "SLAM". It doesn't work. I can pass the OCLT, the water is crystal clear but there's still small pockets of embedded Algae in the glass. As soon as I take a break on brushing for a week or so it's visibly back even with consistent FC > 10ppm (CYA ~70PPM and the SWG keeps the FC > 10PPM all day, every day).

Eventually I'm going to have to re-paint or coat in some way, shape or form but as there's no osmosis and the shell holds water we're kinda trying to stretch it out as long as we can. The shell is 56 this year, so I know it needs some love.

So, background out of the way. Is there an Algaecide that might help deal with the Algae in the glass that I can't get to mechanically?

Back when I was a kid, we had black spot in the pool and I remember every winter dad would add ~50L of acid to the pool. That'd pretty much kill everything. He'd then spend the next couple of weeks slowly bringing the pH back up with Bicarb until it was close enough to start the filter again. I must admit I've thought about it. Surely a really low pH would kill it all

 

[Donldson]

the water is crystal clear but there's still small pockets of embedded Algae in the glass

That's not passing the "clear water" criteria to finish the process. You are stopping the process prematurely.

If chlorinated water can't get in to these pockets, what makes you think that algaecide laden water will?

 

[AUSpool]

Acidifying your water is not a good idea, actually it’s a very bad idea and not something we want a newbie to pick up on from a google search.

If a completed slam and running hot can’t keep you algae free I can’t see how an algacide will either. An algacide is more of a preventative measure rather than a treatment and the copper based ones will add an elevated risk of staining. The algacide recommended for winterising is polyquart? A bit of a guess really.

TFP doesn’t normally recommend this but I would get a phosphate kit with the idea of limiting phosphates.

 

[Bperry]

G'day all,

I have an *old* fibreglass shell. There are considerable portions where the gelcoat is gone and we're down to the glass. The texture of the glass is such that Algae can hide in the texture and it's out of reach of brush bristles. This means no matter what chlorine level I put into the pool, I can't break the skin of the embedded algae for the chlorine to kill it.

Now, when we're at home and I brush the pool a couple of times a week, any accessible Algae sweeps up and the normal chlorine levels kill it. If however I go away for a week or so (like over the Christmas holidays) then I come back to a green film over the bottom of the pool which requires a couple of days elevated Chlorine levels, filtering and sweeping to get back to clear.

Don't tell me to "SLAM". It doesn't work. I can pass the OCLT, the water is crystal clear but there's still small pockets of embedded Algae in the glass. As soon as I take a break on brushing for a week or so it's visibly back even with consistent FC > 10ppm (CYA ~70PPM and the SWG keeps the FC > 10PPM all day, every day).

Eventually I'm going to have to re-paint or coat in some way, shape or form but as there's no osmosis and the shell holds water we're kinda trying to stretch it out as long as we can. The shell is 56 this year, so I know it needs some love.

So, background out of the way. Is there an Algaecide that might help deal with the Algae in the glass that I can't get to mechanically?

Back when I was a kid, we had black spot in the pool and I remember every winter dad would add ~50L of acid to the pool. That'd pretty much kill everything. He'd then spend the next couple of weeks slowly bringing the pH back up with Bicarb until it was close enough to start the filter again. I must admit I've thought about it. Surely a really low pH would kill it all

Test results or logs to share? Hard to say without the data.

 

[Brad_C]

That's not passing the "clear water" criteria to finish the process. You are stopping the process prematurely.

Indeed. How many months do you think are required? I gave up after 3 at Mustard Algae levels.

If chlorinated water can't get in to these pockets, what makes you think that algaecide laden water will?

Chlorinated water gets there just fine, but this algae seems to have a strong biofilm that protects it. Without being able to mechanically disrupt that even mustard algae chlorine levels are ineffective. I was hoping perhaps there was an Algaecide that may compromise the biofilm chemically. I've even tried pouring liquid chlorine directly on the affected areas with a long PVC pipe and funnel. This stuff is tough.

Test results or logs to share? Hard to say without the data.

Right now ? Sure.
FC : 12
CYA : 80
TA : 110
CH : 250
Salt : 4400
pH : 7.35

 

[Brad_C]

If a completed slam and running hot can’t keep you algae free I can’t see how an algacide will either.

That's the problem. I can't "complete" a "SLAM" because I can't get the remaining Algae out of the texture. Short of SCUBA and a toothpick this Algae won't move. I was hoping perhaps an Algaecide would help break up the remaining tough little blighters and at that point I could keep it clear. I'm not looking to use it as a continuous treatment, just a one off to clean up the remains I can't brush away.

 

[Bperry]

Indeed. How many months do you think are required? I gave up after 3 at Mustard Algae levels.

Chlorinated water gets there just fine, but this algae seems to have a strong biofilm that protects it. Without being able to mechanically disrupt that even mustard algae chlorine levels are ineffective. I was hoping perhaps there was an Algaecide that may compromise the biofilm chemically. I've even tried pouring liquid chlorine directly on the affected areas with a long PVC pipe and funnel. This stuff is tough.

Right now ? Sure.
FC : 12
CYA : 80
TA : 110
CH : 250
Salt : 4400
pH : 7.35

Do you keep track of the test results over time? That might help. Having algae that comes back after brushing would indicate lack of chlorine. I’ve had black algae spots in the delaminated plaster spots before it was replastered and a few days of slam cleared it up, no brushing needed. Doesn’t mean you don’t have something different but algae coming back within a couple days sounds wrong.

Assuming your kit is still good, do you normally run the FC about 12ppm?

 

[Brad_C]

Do you keep track of the test results over time? That might help.

I used to but stopped a year or so ago. If the chem is always ok there's no point writing it down. It's pretty stable.

Having algae that comes back after brushing would indicate lack of chlorine. I’ve had black algae spots in the delaminated plaster spots before it was replastered and a few days of slam cleared it up, no brushing needed. Doesn’t mean you don’t have something different but algae coming back within a couple days sounds wrong.

This algae doesn't go away short of me poking it with a toothpick. What happens is it seems to grow slowly. If I brush every couple of days, anything that's on the surface gets eaten by the available chlorine, but the stuff in the glass stays behind. If I don't then there's a slow growing thin carpet across the exposed glass sections of the pool. This algae only seems to respond to mechanical agitation. If I keep the FC > 18 then it doesn't seem to grow, but that gets excessive. It also doesn't remove the stuff in the glass. I even tried scrubbing it with a sock full of cal-hypo one day.

Assuming your kit is still good, do you normally run the FC about 12ppm?

Usually sits between 10 & 13. 13 in the morning after night time filtering and a 5-7am top up, and down to ~10 at the end of the sunny day depending on solar load. The reagents have been replaced twice with fresh chemicals just to make sure I wasn't being fooled.

FC use seems to hover about 2.5-3ppm/day.

A few years ago I used to chase the FC level up and down with the SWG to keep it about 7-8 but turns out leaving the SWG set to 70% the pool kinda levels out at 10-13.

 

[ajw22]

This process works for black algae and may work for your algae problem.

Get in the pool with a weak pressure washer, and you can use that to blast away the algae.

After you have physically disrupted the algae, you should dose it with Liquid Chlorine. Get the strongest liquid chlorine you can find, and if the algae is close to the edges, pour the chlorine down the side where it washes over where the algae used to be. If the algae is all over the place, you can fill a 1-gallon pump sprayer, get into the pool, and spray those spots. And yes, you can do this all underwater.

Then you need to keep your FC at 20% of CYA for the next several weeks.

 

[Brad_C]

This process works for black algae and may work for your algae problem.

Get in the pool with a weak pressure washer, and you can use that to blast away the algae.

After you have physically disrupted the algae, you should dose it with Liquid Chlorine. Get the strongest liquid chlorine you can find, and if the algae is close to the edges, pour the chlorine down the side where it washes over where the algae used to be. If the algae is all over the place, you can fill a 1-gallon pump sprayer, get into the pool, and spray those spots. And yes, you can do this all underwater.

Then you need to keep your FC at 20% of CYA for the next several weeks.

Now, my pool is 4'6" at the deep end, so this process is absolutely genius. I can do it all while standing.

I did try pressure washing the algae at the deep end a few years ago, then laid cal-hypo over it through a long tube, but that didn't deal with the stuff further up the pool which eventually made its way back down the deep end. It only worked there because the cal-hypo could pool in that area. The idea of following it up with a chlorine spray bottle is brilliant. Would never have thought of that. The algae is literally spread in spots all over the pool.

Dosed another 30ppm of liquid last night, put the pool cleaner in and gave it a good sweep, all the accessible algae is dead, so that'll take a few days to clear up back to "TFP Clear". Once it's clear I'll get a fresh tub of liquid chlorine, put it in my 2L "extended wand" garden sprayer, pull out the Karcher with the 10M hose and go to town. My son is going to love this.

CYA is 80, so 20% is 16. I can do that just by turning the chlorinator up to 100% and adding an extra hour a day filtering (in fact that'll get me close to 20). One of the blessings of a small pool.

I started following the TFP method back in 2017 and never had this issue. Back in 2020 we had to move states for 6 months and I came back to a swamp, and I've never managed to get the algae out of the glass since. I just manage it with FC > 10 and regular brushing. That falls down when I go away for > 1 week and come back to green carpet. SLAM until clear + a couple of nights passed OCLT and it's back to manageable. I figure if I can get the algae out of the glass, then as long as I keep the chem in check I could forego a week or two of brushing and not come back to the carpet. I've just never been able to get the algae out, so there's always a seed point for it to restart.

I'm pretty sure in some of the rougher texture I have black spot, so it's a tough combination.

Hopefully next weekend I'll be ready to hit it, so updates to follow.

 

[ajw22]

Note that the drop pH test is invalid above 10 ppm and reads high. So let your FC drop to 10 or below before testing and adjusting pH. Then arise your FC back up.

 

[Brad_C]

I have a calibrated pH meter. I don't use a drop test for pH.

 

[Brad_C]

I got it clear and to the point a good sweep left the water clear, so I got in with the pressure washer to try it out.

It's not a powerful washer and it has to be within 1/4-1/2" of the surface to have an effect, but it blows the black algae out of its hidey holes, and strips the surface of green algae leaving clean uncoloured glass. This is glass I've used a scourer and scrubbing brush (with a Hookah) to try and get it clean and it wouldn't budge.

I suppose the fortunate thing is there's no real chance of surface damage because the washer isn't that powerful. I had a close look at some of the treated area and can find no trace of mechanical damage. The down side is it only cleans strips about 1/2" wide, so there is going to be a *lot* of work.

Today's experiment was about half an hour spot treating the black areas and a bit of the more persistent green. The water is now too cloudy to continue, so I reckon this will take a few weeks, but if I get it right there should be *no* algae left in the surface. If I can reach that point then I'm more confident of being able to keep it that way.

So pressure washer is looking promising. If it gets too close to the surface it gets sucked down hard due to the turbulence so I might try and make a spacer foot for the end and I can just push it around the bottom.

 

[Brad_C]

Ok so the pressure washer is out. I put the cleaner in overnight and woke to a thick layer of glass in the skimmer sock. I can't physically see the damage, but the handful of glass fibres (literally a full handfull) tells me I'm damaging the glass. Back to the drawing board.

 

[Bperry]

Ok so the pressure washer is out. I put the cleaner in overnight and woke to a thick layer of glass in the skimmer sock. I can't physically see the damage, but the handful of glass fibres (literally a full handfull) tells me I'm damaging the glass. Back to the drawing board.

Keep your chlorine up and see if the newly cleaned areas start going green again.

 

[Brad_C]

That's my plan. FC was 19 this morning. It tends to settle between 10&13 so we'll see where it lands.

The clean parts are really obvious, so when it clears up this arvo I'll take a series of photos for record.

 

[PoolStored]

Brad,

We have seen LOTS of black algae. If you want to permanently be rid of the black algae, here is what to know, and our recommendation.

Once BA, always BA. If you don't do the following it will be back.

Run your FC at 20% of CYA for at least at least 4 weeks. That means, if your CYA is 50, you are running at no less than 10FC. You want to be no less than 10FC when you test. If you need to dose higher, so that you are >10 when you test, do that.

This is the part that sucks; run your FC CONTINUOUSLY on the high side, on an ongoing basis, at a minimum 15% of CYA to try and keep the black algae at bay. So if your CYA is 50, run at NEVER less than 8. Better to maintain 10 at all times.

The pool, swimmers and equipment is completely safe up to SLAM level for your CYA. (Slam level for CYA of 50 is 20FC).

On the pressure washer side, for BA, you ALWAYS want to start with the widest degree tip...like 45 Degrees, and start at 18 inches off the pool surface, and likely never get closer than ~12".

Sincerely,
PoolStored.