Coralline algae disappearing?

[PinCave]

I'm running a 72g mixed reef tank. This is being going on for about 8 months now.
I had lots of coralline algae on the life rocks, back wall of the tank, and powerheads. Purple, and red coralline algae. Almost every inch of exposed rock was covered by coralline algae. Everything was doing well.

Last few weeks, I noticed disappearance of the coralline algae on a couple large areas on different rocks. The areas seemed to be have no life; white; cement white. I checked a range of water parameters and everything seemed fine.
Calcium level about 380-400
Alkalinity about 7 or 8
pH about 7.2

Fish and corals continued to do very well.
I'm using Kalkwassler water in an automatic top-off system for calcium replacement.
I'm puzzled why the coraline algae disappeared.


Pin

 

[PinCave]

error
the pH was about 8.2

 

[atkinsg]

I think your alkalinity may be a little low. I know I see coralline bleaching when the alk. gets below about 9dKH

 

[bertoni]

7 is on the low end of acceptable, from the chemistry forum, so that might not be a problem. Do you have a magnesium test result?

Does the area look bleached or eaten? Maybe some coralline eater is getting large enough to be noticed. Just a guess.

 

[PinCave]

I'll try to get the alk up a bit.
I don't have magnesium test kit. I only use Kalkwassler. Never added any magnesium nor iodine. Should I?

The area looks bleached; completely.
Is there such thing as coraline eater? some kind of snails?

 

[bertoni]

Various animals eat coralline. Urchins are one possibility, for sure. Maybe some snails, too.

I would ignore iodine, but magnesium is worthing testing once a month or so, IMO.

 

[PinCave]

I don't have any Urchins as far as I know. Several small snails came with live rocks.
I said it looks like bleached because the area is completely bared, without a speck of coralline algae. The border with coralline algae is sharp.

Thanks for the suggestions. Something for me to work on.

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[billag]

Did you ever figure this out? I'm having the samething happening in my tank. Very similar parms to yours. It's just disappearing, not bleaching, disappearing. The back of the tank is becoming bare glass.

Only snails I have are turbos and nassarius. Maybe there is something lurking that only comes out at night ...

 

[PinCave]

I never completely figured out what happen.
I did bring up the alkalinity up a bit.
The problem seems to be resolving; at least not worsen.


Pin

 

[drock59]

Asterina starfish? Little tiny, tan in color? They eat coralline. Just wondering cuz i have them and have a serious lack of coralline.