Weird algae location

[KenRexford]

For 15 years I never had GHA. Most of that period was FOWLR with horrible parameters I am sure. Now, with great parameters and my game up, I have none of the old algae but now GHA. Even my calcareous algae has changed from green and red (all gone) to lavender. So, I am convinced that GHA is a sign of success in a manner of speaking.

What is weird, though, is that the GHA is aboit 90% on the right half of the tank. Flow is good. Lighting is identical. But most of the GHA is on the right. What on earth could cause that sort of segregation?

The tank is of course not entirely identical on both sides. The differences:

Protein skimmer (HOB Reef Octopus) is on the left, but the rare GHA on the left is near the skimmer.

Overflow is in the left.

The only fake pieces (shipwreck, fake liverock structure) are on the right. (My fish love hiding in the shipwreck, 16 years going.)

My operating theory is that the shipwreck might be taking longer to leach reserved nutrients from years of poor husbandry and therefore that it is just a matter of time until the right side GHA also clears.

Thoughts?

 

[eric.tech]

I had a similar issue on a younger tank, about 6mo old. All my parameters were spot on, low amount of live stock in the tank and i had GHA spreading like wildfire. A good friend suggested what you were thinking, the rock may be harboring nutrients allowing the GHA to grow on it. It was in my case. If your parameters are in check and there's not a lot of detritus settling on the rocks/GHA, it'll probably dissapate in time. I went with the more labor intensive removal of rocks. Cleaned them with a brush and a peroxide/water mix. I also increased flow in the tank and at the specific areas of concern. Hope that helps!