Any alternatives to treating black algae?

[rlsnights]

We have been trying to rid our pool of black algae for almost 3 months and I have hit the wall here.

Part of the problem is that I let our FC level drop down below 20 after being told by several folks on here that it was OK to do so because our overnight FC loss had dropped to zero. Well the algae came roaring back and is now much worse than it was to begin with. Plus my spouse (the only one physically able to brush the pool) is having to work overtime a lot and we are not able to brush the pool more than once a day and occassionally not even that.

I have raised the FC level to 35+ and have nagged/bribed/whatever to get my sweetie to brush the pool every day for more than 3 weeks and it is making no visible difference. I am spending $100+ a month for liquid chlorine. I am having to add 2+ gal of chlorine a day to keep the FC at 35+. We are using a SS brush.

We can't keep this up any longer and I don't want the algae problem to get worse. So what do I do?

If we drain the pool and let it sit dry will that kill the algae? If we drain it can we wash the spots with bleach to kill it?

Patricia
15,000 IG White Plaster cart filter jet vac sweep

FC 38
CC 0
pH - no reliable #
TA 120
CH 150
CYA 55

 

[JasonLion]

There are various other things you can try, but they are all a substantial amount of work. Some people have had success pressure washing the algae off with water in the pool and high FC levels. A complete drain and scrubbing with bleach will usually do it, but it is easy to miss spots, requires lots of water and effort, and can cause serious damage if you have a high water table and don't take the right precautions. Some people have had success rubbing each spot of algae with a trichlor tablet for a couple of minues, but this can get tedious quickly if it is all over.

 

[chem geek]

Other than high chlorine with brushing or applying Trichlor directly to the spot (along with brushing), the only other way to get rid of black algae is with a specifically targeted algaecide (along with brushing), but unfortunately almost all of these against black algae contain copper. The downside is that copper can stain if too much is applied or if the pH rises and staining is particularly a problem in plaster pools. That's why this isn't normally recommended on this forum. The other approach, which would be a last resort, would be a phosphate remover if the phosphate levels were high, but that would only prevent future growth and would not remove existing algae. I am NOT recommending these approaches -- read on for what I believe may be happening.

Something about your situation doesn't make sense since a CYA of 50-60 ppm shouldn't have the algae "roaring back" if the FC didn't get very low (say, below 5 ppm). In this post you said that is was Leslie's that did the CYA testing which said the CYA level was 50 ppm and that the test kit we suggested was $100 at Leslie's. Based on this post and this post it sounds like you purchased the FAS-DPD test kit from tftestkits.com so you could test high chlorine levels, and to supplement your less expensive test kit BUT it seems to me that you don't have a Cyanuric Acid (CYA) test in your test kit, is that right? Otherwise, you wouldn't be relying on Leslie's for the CYA test. I believe (based on your first post) you purchased Leslie's Deluxe DPD test kit shown here which does not have a CYA test.

I'm just wondering if you've ever tested the CYA level yourself, using your own test kit. Pool stores often perform tests incorrectly, especially the CYA test. If you don't have a CYA test in your test kit, then the CYA test will tell you if your CYA level is actually still very high, even 100+ ppm, in which case that would explain why it takes 20+ ppm FC to prevent the black algae from growing fast. If in fact the CYA level is still very high, then more partial drain/refill to lower it should have been what was done first.

According to your first post here, the CYA level measured at Leslie's was 220+. You then did a drain/refill, but didn't say by how much, but Leslie's measured the CYA at 100 ppm which would imply draining at least half of the water (is that what you did?). Then later tests by Leslie's showed CYA at 70 and then 50. However, nothing was done that should have lowered the CYA level by that much (i.e. no drain/refill) though the chlorine level was high so after a longer period of time the CYA might drop, but not in the few days between Leslie's tests. Also, by any chance was the "pool shock" that Leslie's sold to you called Chlor-Brite as shown here? If so, then that is Dichlor where for every 10 ppm FC it also increases CYA by 9 ppm. If you used (as stated in your first post) "4 bags of shock then 2 bags daily for as long as it took combined with brushing", then you would have increased your CYA level quite rapidly.

Richard

 

[rlsnights]

Hi Richard,

Thanks for the long and thoughtful reply.

Yes I finally was able to afford the full DPD test kit and have tested the CYA myself. This is a VERY subjective test but I would say that my CYA level is no higher than 60 and it seems to me to be closer to 55.

We drained and refilled the pool a total of 3 times to get the CYA level down this low. The first time I relied on Leslie's to test the CYA level but when they tested it again and gave me such different results it was clear to me I needed to test the water myself. So I did and got a CYA level of 120 so I drained and refilled the pool 2 more times until the CYA was down to 55-60. I think this is a pretty accurate CYA level.

Yes the original shock they sold me was the one you mentioned, thus the increase in our CYA level when I was trying to lower it :grrrr: But I fixed that once I understood what I needed to be testing and that I needed to go to liquid chlorine to treat the pool.

So the CYA level was OK before I let the FC levels start to drop below FC 20. I started dropping the FC levels despite the continuing visible algae spots because that seemed to be the advice I got here. The overnight FC levels had stopped dropping and the daytime loss was minimal at that point.

The renewed growth of the black algae with some new spots came after I let the FC drop down to around 8 based on the suggestions I'd gotten from others on the board. Also we have had a hard time sweeping the pool as often as we did at first - sometimes skipping a day. I know the pool didn't get swept the 2 days I had to be gone 3 weeks ago when my mom was in ICU and the FC levels weren't tested while I was gone either. The FC when I got back was down to around 15.

So I realize that part of the issue is that we need to be more consistent with keeping the FC levels high and doing the brushing in order to see a big improvement. But since I came back to the board and got clarification about continuing to keep the FC levels very high I have been doing my best to follow those suggestions. It just doesn't seem to be making a difference and my spouse is getting really unhappy about having to sweep the pool in the dark and we are having a hard time affording the chlorine at $25+ a week.

I know the algae is eating the chlorine because we are losing so much chlorine over the course of a day since I started doing FC 35+ again. The FC has been dropping by as much as 15 over a single 24 hour day when I was only seeing a drop of 3-4 over the course of a day before.

The only other issue is that our CH is kind of low and I haven't been able to get to the store to get the stuff needed to raise the CH level a bit.

Patricia

 

[chem geek]

Thanks for the update. Having the algae, especially black algae, come back strongly with an FC of 8 and CYA of 55-60 is strange. It's important to knock off the slime layer ("heads") of the algae to expose the chlorine to algae that is underneath, but you've been spending a long time doing that by brushing as well as having high chlorine levels. Certainly you are spending more time, money and effort than one would want.

What was the Black Algaecide that you used? Was it Black Algae Killer shown here? If so, then this was an algaecide with copper in it (it's contents are shown here). It's possible that heavy use of a copper-based algaecide followed by heavy shocking without lowering the pH first could cause copper staining which can also appear black or dark green (see here or here), but such staining would happen when the FC (really, the pH) was high, and not increase when it dropped lower as you had seen.

Black algae looks like the photo in this link (where you need to click enter in the URL entry area if clicking on the link says "Forbidden"). Another example on steps is here. Is this what your algae looks like?

Did you ever try putting a Trichlor puck on any larger stain to see if it faded?

Richard

 

[rlsnights]

No I haven't tried the Triclor tablet - somewhere I read that it could damage the plaster and it was never before suggested on TFP. I can try that and see what happens. How long should I leave it on one area?

Also I will retest the CYA level again. The directions say when the dot disappears to stop adding solution but I can still see the black dot dimly through the white solution for a long time before it finally completely disappears. Is this the right way to judge it? Or should I be calling it when the black dot first becomes somewhat hard to see?

I'm not sure but I think that was the Black Aglaecide I used. But it's clear to me that these are not copper staining - we have new spots that just appeared 2 weeks ago and it's been at least 4 months since I put any algaecide in the pool plus I've drained and filled over 2/3 of the water in the pool since I used it.

After looking at your photos I have to say I may have overstated things when I said it came "roaring" back. We don't have anyplace in our pool that looks even remotely like the photo of the steps you posted. Yikes - I'd be scared stiff if it did. And the spots we have are mostly small - the diameter of a pencil eraser or smaller - scattered all over the pool but concentrated most on the steps and along the southern side of the pool that gets the most shade. Guess what I should have said was that we now have more spots than before and in new places like the deep end of the pool.

The biggest spots are new ones in the 9' deep end of the pool so it's hard to tell for sure how big they are. I'll take a photo of some of the spots and try to figure out how to post it for you to see.

I'm pretty sure it's black algae because sometimes when you brush a spot it leaves a black smear across the surface where you just brushed. That and the fact that we keep getting more spots - not less. Also that we're losing so much chlorine seems to suggest it's something organic going on.

I think the biggest problem is we're just not brushing the pool often enough. Sadly this is not really under my control and my sweetie is getting very worn down by how long this has gone on and on and on. We joked tonight about filling the pool in and starting a garden there instead, (using child labor to do all the work of course ) and we were only half joking...

Frustrated in Sacramento,

Patricia

 

[JohnT]

Also I will retest the CYA level again. The directions say when the dot disappears to stop adding solution but I can still see the black dot dimly through the white solution for a long time before it finally completely disappears. Is this the right way to judge it? Or should I be calling it when the black dot first becomes somewhat hard to see?

When you can no longer see the dot.

 

[chem geek]

The photos in this link may be helpful for your CYA test.

Well, I'm really sorry about your situation and am still suspicious about what it is. Black algae is slow growing and it looks sort of crusty like the photo link I showed you. It isn't normally a perfect circular spot with fuzzy edges -- that's more typical of metal staining. You are right about the overnight chlorine loss implying something organic.

If you have or can get a Trichlor puck, then you can place it over an area with a larger spot. You are right that it will tend to lighten the plaster in the area -- I have one such lighter "trichlor puck sized" circle in my own plaster pool where I checked on what turned out to be a metal stain (iron, in my case). If you rub (scrape) the Trichlor into the spot rather than leave the entire tab on the spot, then there will be less of a mark, but it will be harder to tell if the spot fades. So if you've got a place where having a slightly lighter circle of plaster isn't a problem, then you can try this, but that's up to you.

Unless someone else comes up with a good alternative, I'm about to suggest some last-resort methods including a phosphate remover (though you'd have the water tested for phosphate level first -- was that ever tested and if so, what was the level?).

Richard

 

[chem geek]

If you have or can get a Trichlor puck, then you can place it over an area with a larger spot.

A modification to that idea would be to carefully chip off a smaller piece from a Trichlor puck that you can place on the spot. That will make any lightening of plaster in a much smaller area, probably not even noticeable if the chip is about the same size as the dark spot. I wish I had thought of that when I did the Trichlor test in my pool years ago, though the whitening isn't a big deal for me.

If you use the smaller piece as above and can somehow make sure that it stays on the dark spot (a smaller piece is more likely to move from flowing water) then leaving it on the spot for one day should show a significant lightening of the spot if it's algae. Scrape the spot with a metal brush first, before putting the Trichlor on the spot.

 

[Guest]

You can also get granular trichlor from the pool supply. It's purpose is to treat black algae but it will cause your CYA to rise.

 

[rlsnights]

Ok, so I tried the puck on a spot but I had to leave and my pump came on so the puck was several feet from where I'd left it when I came home. Tonight I bought some granular trichlor to try on Friday (out of town tomorrow) when I can be home all day and figure out a place to try it where it won't get washed away too fast.

I re-tested my water and got some new readings that only increase the mystery as far as I'm concerned. Here are the numbers as of this evening:

FC 24.5 (down from 35 the night before)
pH 7.8
TA 140
CH 140
CYA 35 (down from 55) :?

We've had 2 rainstorms come through since the last time I tested the CYA and our water level is up so high that, after today's storm, I'm going to have to drain some off on Friday. Do you think that's the reason the CYA level has dropped so much?

Does the low CYA level help explain the high Chlorine loss?

Happy Thanksgiving everyone. I'm thankful for your help :-D

Patricia

PS: I finally got help really measuring my odd shaped pool and have revised my estimate of the number of gallons in the pool up to 17,000 from 15,000.

17,000 gal IG white plaster cart filter (new last year) Jet Vac sweep new pumps this year