Some thoughts and questions on black algae control

rtilghman

Well-known member
Nov 19, 2014
52
Austin, TX
First, I've searched the forums, and I've read previous posts about black algae (some quite old). However, I haven't found exactly the conversation I'm looking for... so here goes.

I live in Austin, TX, with an in-ground pool with glass tile, epoxy grout, and a pebble mix plaster (name escapes me). As southerners already know, we don't close our pools here, so managing chemistry and algae are a year round fight. A couple of years ago I started seeing pockets of black algae forming on some of the grout... specifically on horizontal surfaces (steps, ledge).

I began fighting it by brushing and shocking the pool, but while that manages the green algae and other issues the black algae is largely impervious (unless I shock for weeks). A wire brush might help, but since the algae is on grout between glass tiles that's a nonstarter. I upped my game by using a handheld thinset saw thing to grind at the black algae, but that was time consuming and largely ineffective.

In a bid to win the war I started scrubbing with trichlor pucks, but that was only lightly effective... getting in the crack on the grout is hard, and the short exposure didn't really kill the algae. So, I switched to just taking pucks and sitting them on the tile/grout for days. THAT worked, so I slowly moved them around until all the algae was visibly gone. The only issue is that the pucks have a fixed shape, and they dissolve very slowly, meaning it takes awhile.

Recently I decided to try something new... I took some filter socks I have from a previous experiment, filled them with clorox trichlor granules, tied them up, and set them on the algae. THAT worked fast... I see progress in hours, with the algae just vanishing.

Okay, context provided, I have two questions for the assembled minds on this board.

1) Is there a downside to using the granules? I ask because obviously they dissolve quickly... I use LC and manually manage my CYA, so I should be able to keep that in check (around 40 now), and I test my chems regularly and will monitor FC. However, I'm wondering if anyone has any thoughts on using granules like this.

2) I've noticed that after the trichlor kills the algae my epoxy grout is a little bit yellow-ish... is there a reason why? It's a little like a synthetic shirt you bleach in the wash... is there a way to manage this or return it to a whiter/clearer appearance (my epoxy is starlike crystal grout for those interested, which is translucent).

3) Finally, does anyone have better ideas or thoughts on managing black algae I haven't thought of? Note that I manage my chems pretty actively and keep my FC up, the black algae just seems to be an unavoidable component of my environment.

Thanks in advance for any help!

Best,
Rick
 

YippeeSkippy

Mod Squad
LifeTime Supporter
Jan 17, 2012
15,976
Evans, Georgia
Rick, you know us- the first thing we want to see is a full set of current test results-
FC
CC
pH
TA
CH
CYA

You know that the granules are adding chlorine with either CYA or calcium. So you have to be able to absorb that without spiking up too high?

Ok, you say your using liquid chlorine...that's great! Which test kit do you use?

Maddie :flower:
 

JJ_Tex

Gold Supporter
Bronze Supporter
Jul 17, 2019
2,316
Prosper, TX (DFW)
Pool Size
13000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Hey Rick, the "secret" here to preventing algae is to always maintain your chlorine at the correct levels for your CYA. There is a chart in my signature for reference. I've always abided by that and have never once had a speck of any algae in my pool.

What is your FC level currently? Per the chart, for a CYA of 40 you should be at a FC of 5-7 and never ever ever let it get below 3.

As for your specific questions on scrubbing black algae, I'll let others answer that. Have you tried scrubbing the stuff on the tile with liquid chlorine and a stiff brush?
 

Katodude

Silver Supporter
Aug 22, 2017
1,286
West Palm Beach/Florida
Pool Size
15000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-15)
So a couple of thoughts, having dealt with black algae before.

First your trichlor granules sounds interesting. However, double check on the Clorox brand as that usually has copper in it and you dont want that. Make sure you use pure trichlor.

That being said, here is what I do. I take a bamboo BBQ skewer and pick at the black algae until its gone. Then I use as high concentration of LC to pour over the spot that I just picked at. Just to make sure that I killed whatever was their. Its a bit of balancing act as the LC is heavier than water but still will get diluted before it reached the entire area. However, it does have an effect of providing a jolt of chlorine of the newly exposed algae spot. I may add your sock full of pure trichlor to this practice to be sure.

Now, here is the really important part. I now run the FC hot. My minimum target is 10% (thats the bottom, not the target) of my CYA, but I run higher more like 12% (this is with a SWG). If I did not have a SWG I would run even higher, but with a SWG this is working for me. With my FC running hotter than the standard recommendation my pool is pristine.
 
  • Like
Reactions: hecicohn2021

rtilghman

Well-known member
Nov 19, 2014
52
Austin, TX
Thanks for the replies everybody.

So, I appreciate the chems question, but it's not relevant. I know how well I manage my chems (I'm well versed in the CYA table, etc), and I've dealt with it enough that I accept the fact that I have black algae in my pool. Basically I'm not looking for guidance on "how this got in my pool or how to prevent it", this post is just about "dealing with it" once you have it.

In terms of the granules, the product I used is Clorox's All-In-One xtrablue chlorinating granules. No copper (I purposefully avoided the fungicides for that reason), it's just 53.5% trichloro-s-triazinetrione and 46.5% "other ingredients" (I assume largely stabilizer and maybe some filler, etc).

I do have one additional note to provide from this experiment from anyone reading this in the future... use multiple socks. I went out to check things 3-4 hours after I had put it in the pool and the granules seem to have eaten holes through the sock! Ugh, what a mess. It's possible the sock got caught on something and ripped, but given that both the ones I used had this problem (socks were perfect going in) I'm inclined to believe that the trichlor was so strong it annihiliated my socks. So, make sure whatever you put the granules in is strong enough to resist the trichlor's disintegrative powers.

I will say that the granules are a rapid and effective way to kill the black algae. Now I just need to figure out how to address the yellowing of the treated epoxy grout.

Best,
Rick
 
Last edited:

Donldson

TFP Expert
LifeTime Supporter
Jun 12, 2009
4,700
NW Ohio
In terms of the granules, the product I used is Clorox's All-In-One xtrablue chlorinating granules. No copper (I purposefully avoided the fungicides for that reason), it's just 53.5% trichloro-s-triazinetrione and 46.5% "other ingredients" (I assume largely stabilizer and maybe some filler, etc).
The extra ingredients is mostly baking soda to counter the insane acidity of trichlor. It probably also includes some copper as Clorox has told members here before that all XtraBlue products has a small amount even if it isn't specifically listed. Stabilizer is never included in "other ingredients", it's just a part of the trichlor molecule.

The acidity of trichlor is likely why you're seeing results quickly. You're creating an area of very acidic and highly chlorinated water which is killing and then bleaching out the algae. This works, but you're making things worse in the long run. That acid is going to eat away at the holes that the black algae grows in, making it an even more ideal place for the algae to grow and even harder to kill it.

So, I appreciate the chems question, but it's not relevant.
It's always relevant. We'd be rather foolish to just take everyone's word that things are fine with their water chemistry and there's nothing to worry about, now wouldn't we? Generally the only reason someone balks at such a simple request is because they either aren't properly testing or they know their numbers are off and can't admit it. So why don't you post them up?
 

rtilghman

Well-known member
Nov 19, 2014
52
Austin, TX
@Donldson
The extra ingredients is mostly baking soda to counter the insane acidity of trichlor. It probably also includes some copper as Clorox has told members here before that all XtraBlue products has a small amount even if it isn't specifically listed. Stabilizer is never included in "other ingredients", it's just a part of the trichlor molecule.
Interesting... I didn't realize that about xtrablue (miniscule amounts of copper), I'll have to keep that in mind. I can't believe they add copper to a pool product without listing it explicitly... that's crazy given the negatives of adding metals to the pool. I wasn't excited about using a Clorox product, but I was in a rush and it was the only trichlor granule product that the big box store had that fit my bill.

The acidity of trichlor is likely why you're seeing results quickly. You're creating an area of very acidic and highly chlorinated water which is killing and then bleaching out the algae. This works, but you're making things worse in the long run. That acid is going to eat away at the holes that the black algae grows in, making it an even more ideal place for the algae to grow and even harder to kill it.
That makes a lot of sense. I'm a little surprised because I feel like I didn't typically see that kind of reaction with the trichlor pucks I used to use (both for the pool generally before switching to LC and sitting on the black algae), but maybe it's just because it dissolves faster in the granules so the concentrations are higher? Something to keep in mind I guess... thankfully I don't have to do this frequently (once every 1-2 years) and thankfully it's just on the epoxy grout and glass tiles (which are both extraordinarily tough).

So, is there a "purer" granulized chlorine product you would recommend than trichlor granules? Note that I considered cal hypo, but I'd like to avoid adding calcium, if only because we live on a limestone mountain and I already run 275ppm by default (calcium is not my friend). I guess sodium hypo might be an option, but isn't the AC really low?

It's always relevant. We'd be rather foolish to just take everyone's word that things are fine with their water chemistry and there's nothing to worry about, now wouldn't we? Generally the only reason someone balks at such a simple request is because they either aren't properly testing or they know their numbers are off and can't admit it. So why don't you post them up?
Haha, fair point. I guess because it always irks me on forums when someone asks a specific question and instead of answering that question regulars quickly post stuff that doesn't really address what was asked. I used to run a networking forum and it always exhausted me... like somebody would ask about a specific networking problem and the FP is "did you try restarting the computer?" Not being defensive or criticizing anyone, just a personal pet peeve.

Thanks,
Rick