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My anubias has started growing little dark brown fuzzy spots on its leaves. I don't see it anywhere else. Unfortunately, I can't seem to get a clear picture that I could post. I'm guessing it's either diatoms or BBA. How can I tell the difference? Would it be best to just replace the plants (it's on two of them)?

I was keeping the light on for 10 hours, but am cutting back to 7. I suspect my T8 8000K light is too intense, so I'm considering something like a Finnex Stingray. YouTube reviews say it isn't overly intense, and its higher position from the water surface should help too. Would that be a good first step in getting at the root of this algae? The aquarium doesn't get direct sunlight.

It just occurred to me that the highest anubias leaf, which is just a couple of inches from the light, was the first to have the algae and has the most. It's clearly the light. I'm going to switch out my black hood for a clear top and will order the Finnex. I'll try treating the plants and see how it goes.
 

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From what you describe they seem to be diatoms. Diatoms will usually rub of easily from plant leaves. BBA will be very well anchored and it has vertical growth, not just a flat spot. BBA will also be more blue/purple or red. Diatoms are usually brown in color.

It has been suggested that one factor that brings BBA invasion are high level of organics. While diatoms are typical for new aquariums and water with high Si content. Regardless, algae in one part of the tank is likely to show up in other parts. Removing the affected leaves might be a good way to remove the algae, but you also need to remove the reason they grow. BBA is easily killed by spot dosing liquid carbon (Excel)

I am not very sure that the light intensity is very high as T8 are not that efficient with power. It is good that you reduced the light duration.
 

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Discussion Starter · #3 ·
Thanks, dukydaf. It seems the spots were diatoms. They were definitely brown-black. I used a paintbrush to remove them during a partial water change today. Some of the spots took a few passes, but they all came off without any visual sign that they were ever there.

The light looks awfully bright to me, but I know its intensity is at the low end of the scale. Still, I wonder if a horizontal leaf surface being just an inch or two from the light is too much. If nothing else, it has always looked a bit harsh to me.
 
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