Is this algae?


Active member
May 26, 2020
Canberra, Australia
Settling in to around 10 months of pool ownership and I like to think I have the basics worked out now and generally maintenance is going well.

I have started to get what looks like algae growing in the tile grout. The brownish/black spots you can see in the grout. Though this is only growing on the bottom of the pool, not on the sides. It cleans off pretty easily with a steel brush. I do get a lot of leaf litter in the pool. At least 1 full basket every week. I brush and manually vacuum the pool at least once a week but the leaf litter can sit there for a few days until I get to it, I am wondering because it is only on the bottom of the pool if the organic leaf litter is causing this?

My questions are:

Does this look like algae, maybe black algae or could it just be staining from the leaf litter?
What is the best way to manage it? SLAM?
I brush the sides often but I don't always brush the bottom of the pool but it does get vacuumed. Should I brush the bottom more frequently?

I did a OCLT last night and no drop in FC at all and even saw CC drop from 0.5 at 8pm to 0.0 at 6am
The pool is still very clear, the photo was taken at the deep end of around 2m so you can see the water is very clear.
My pool math logs should be available to view, let me know if you cant see them.

Any guidance on how to treat this would be appreciated




Active member
May 26, 2020
Canberra, Australia
ok does anyone know how to make my PM logs visible?

FC 5.5
CC 0.0 (0.5 yesterday)
pH 7.6
TA 60
CH 400
CYA 60
SALT 3600

I only have a manual vacuum, no suction cleaner or robot, so its just brushing and a manual vacuum once a week, twice a week if its windy and I get more debris.


Active member
May 26, 2020
Canberra, Australia
I think I have fixed my issue so my PM logs should now be viewable.

I am hoping someone knowledgeable can confirm that this is just staining, the fact that it only appears on the bottom of the pool not the sides, plus the fact it is only in the grout and not on the tile itself and a passed OCLT means this is just staining.

I guess I will begin brushing and vacuuming daily and see if it stays away?


Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
Laughlin, NV
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Staining from an organic source should be removed with chlorine. It will be difficult to get at the stain as the grout is porous.

Try holding your FC at mid way between Target and SLAM for awhile, with vigorous brushing of the grout lines on a regular basis.

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