You can increase the flow to better reach these areas, reposition your current flow to better reach these areas, or you can dwindle down the variables to try and find the root cause of this issue. I suspect this is possibly cyanobacteria which typically presents itself in tanks that may have high nutrients.
Do you have a gauge on your parameters so we could confirm?
If you do indeed confirm it's cyanobacteria and would like to lower your nutrients, then you could try skimmer wetter, or better yet - getting a check on your feeding habits and the foods you're using. Cutting to once or twice a day and using foods that are of the highest benefit with the lowest pollutants (such as frozen) would help tremendously. Another option is to alter the photoperiod.
Best of luck to you!!! I'll keep my eyes peeled for an update from ya
Hey thanks tsouth ya I have parameters as ph 8.2 nitrates are 0 or very low ammonia is 0 salinity is 1.25 I have a nano slim skim hydor protein skimmer and a hang on carbon filter with bio media
Looks to be just black looking maybe dark purple patches and have a ton of micro bubbles from my protein skimmer that it’s been putting off for 3 weeks
I’m going to go with cyano. Hopefully the tips above will steer you towards success. FWIW there are chemical treatments but I think a little tweaking on your end can make this an easy battle.
Feel free to share your feeding habits and we can see if there’s any improvement to be made there.