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Greasy brown coating on Cardinal Lobelia.


Community Member
Jul 19, 2023
I am guessing it is some sort of Algae. It is mostly only forming on the Cardinal Lobelia plants and glass.

I have been rubbing it off leaves and snipping the ones more covered. I have cut off clean top growth and replanted while discarding lower coated growth.

None of the other plants seem affected. It is only in 1 tank.

does anyone know what it is?
Its not a new tank though. Well over a year old. 60-70% water changes weekly. Nitrates targeted to 20 ppm. Only really forming on the cardinal and glass pipes.
I had this exact diatom problem with this exact plant (and others) in my old setup. My substrate was beyond filthy with muck. I decided to replace the substrate rather than spend the time vacuuming out all the junk that was built up in it.

Giving your substrate a good deep vacuum over the entire area a few times should. @GreggZ and @Joel Armstrong both did deep substrate cleanings and could help more with the specifics. I went the shop vac route.
Well, I largely replaced the substrate with rescape 8 days ago.
Ok. New substrate equals young/new setup.

I had diatoms for a few weeks after I replaced my substrate entirely. They didn’t last long though. A month tops. Nothing like I had before the change though

It should go away with time assuming everything is clean and stays that way with the new substrate.

What did you was there and what did you replace it with?
I had a fair amount of Safe T Sorb capped by an inch of BDBS.

Over the course of a yearor so, too much safe t sorb had migrated to the surface. I pulled out about 5 gallons of substrate.

I left about an inch of Safety sorb in the middle and back and capped with a good 2.5 inches BDBS.

I also removed a lot of Anubias and Java moss that had come to dominate the tank.

Just an update.

I gave the tank a thorough cleaning a little over a week ago, pulled all the rocks and soaked in peroxide and scrubbed and returned, cleaned out the filter and piping and all the glass. Pulled affected plants and soaked them in seltzer water overnight and returned in the morning.

Been free of the brown gunk since then.