No purple/red coralline algae

Hi, I have a few tanks using ats.
Why are most of them void of purple coralline algae?
At the best , there is a little coralline algae. Any reason?
Thanks for sharing your thoughts n experience :)

It is usually because of high phosphate. Have you tested?

haven't tested though. no signs of slime but rocks are covered with green algae that tangs n rabbitfish love.

Just tested my phosphate '0'

Pics of the rocks would help.

Pic....a lot of green but few spots of coralline algae. Attachment 6398Attachment 6399

Ok this is a simple case of phosphate soaked rocks. Once you export enough, the algae on the rocks will let go and be replaced by periphyton (including coralline)

Thanks SM . appreciate it.
Questions 1. i realised i havent been consistent with keeping my bulbs at 3months old. the last time i changed bulbs was 6months ago. i believe this has caused my rock to soak up the excess N and P. is this correct?

Q2. how can u tell if its phosphate or nitrate soaked rocks ?

Thanks again.

If you don't export enough, the phosphate must go somewhere... such as the rocks. Thus gives fuel to the algae on the rocks. Without that fuel, the algae cannot hold on. After it lets go, coralline will fill in.