Help, please...identifying an tackling an algae issue

Greetings!!!

I've researched plenty online and been to more than one LFS and still having an algae issue -- may be with identification not just approach to solve. I have a 90g CA/SA tank with an Oscar, Jack Dempsey and a Severum as the main attraction, but also have a Blue Acara and a spotted pleco (4-5"). So yes, fairly high bioload but also filtration is high. My tank is near a window, and unfortunately cant do anything about the location. I have been having a problem with what I believed for the longest was just brown algea/diatom when my africans were in it (prior to this, this tank was an african peacock/hap tank). Now I'm questioning it. I dont get so much of the brown film on the glass any more, but large sections on the 3D background and on the fake driftwood decor show a dark black, somewhat greenish caked layer of what looks like dirt and I havent been able to get rid of it. It began as light brown (like diatom), and over time got darker and darker. Based on research and what I was told, I treated as if it was diatoms due to high phosphates (and silica), and now was just told by another LFS they thought it was blue-green slime algae. That didnt sound or look right to me, but I'm not an expert on that, cyano and the like and dont maintain a saltwater tank where a lot of that seems to be more prevalent.

I tried:
1. VIbrant (freshwater) for several weeks... it seemed to lighten after a few weeks, but then came back and darkened.
2. My phosphates from the tap are kind of high (1 ppm), so I have been running pure GFO, along with carbon and purigen, and have used Phosphate-E, which does reduce the PO4
3. I always do a 50% weekly water change, but did a couple mid-week changes just recently to bring nitrates down further
4. UltraLife Blue-green slime remover (first dose this week as of the new identification)

I test PO4 and NO3 regularly now since I've been at this. I use Hanna checkers for these and as of this weekend, my PO4 was at .23 ppm and NO3 is at 24.5 ppm before this week's change.

Filtration:
1. Fluval FX6 -- running ceramic rings and Matrix
2. Aquaclear 110 HOB-- running GFO, activated carbon, purigen, and filter floss

Attached is picture.... of the decor and the black crud in the background....

THANK YOU in advance!!! I really just want to know what I'm dealing with and the best way to tackle!!!!

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A201 -- I'd like to tag you on this one as well. Thank you so much for your advice on a post I made last year when I was re-doing this tank:
Oscar filtration options - 90 gallon SA tank | Cichlid Forum | 501132

I went with the Oscar, of course as well as a JD, and went with your recommendation of the AC110 (those were always my go-to as well) along with my FX6 rather than 2 canisters again. Obviously I have a combination of nutrients, etc. that are making this tank a problem, so was hoping you might have some additional pearls of wisdom on this with your cichlid experience....

thanks!!

 

Get a big Pleco!

And some blinds for the window. Or put some opaque paper on the sunny side of the tank to block the sun.

 

I agree with blocking some of the natural light. For actually getting rid of the current algae, I recommend taking an unused toothbrush to it and just scrubbing it off and/or a 1-2 week blackout to get rid of any remaining.

doesn’t look quite like Cyanobacteria to me, but I could see how it looks similar.

 

Frank the Fish guy and Cue thanks for the input.

Well I have a spotted pleco now, and I've had a large bristlenose before with my African peacock tank but he died. The pleco doesnt spend a lot of time on the 3d background... I assume the rough, rocky texture, and he doesnt seem to be eating much from it.

I also can't blind this window completely. We hare large curtains in from of the main part of it, but it's a front living room window with an arched top --- curtains dont cover that part. I HAVE wondered if lightly tinting the window would solve the problem -- block enough light to make a significant difference without making the room too much darker?

My concern right now is knowing WHAT this is so I'll at least know the options. I thought for sure it was all diatom before. Attached a new pic with different lighting..tank lights on, no sun and no reflection.

 

Are your fish big enough that they would eat Nerite snails? If not, then Nerites will eat this algae. Looks like algae to me.

Nerites are the best algae eaters!

 

+1 on the nerites- they make mystery snails seem lazy!

 

the Oscar is about 8 inches in length and can eat small shrimp...not easily but he can get the whole thing in his mouth. I saw him attempt to eat a small rock in the tank once (and spit it out). When I did have a few mystery snails in with my african peacocks and clown loaches once, they never stood a chance. They were picked on constantly by the cichlids and dead or eaten from their shells within days -- eaten probably by the clown loaches. Because of all that and what I have read on forums like this about oscars, I never bothered trying to put in nerites with this tank.

To me, seems like nerites and mystery snails are more of a community tank inhabitant.