Black dust looking stuff.

Colin_T said:

Hi and welcome to the forum

It could be the start of black beard algae. Take the plastic plants out and soak them in bleach for 10-15 minutes, then rinse them off really well with tap water. Put the rinsed plants in a bucket of tap water and add a double dose of dechlorinator. Swirl them around and leave for 5-10 minutes, then rinse again and put back in the tank.

Do a 75% water change and gravel clean the substrate every day for a week. Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

Wipe the inside of the glass down and clean the filter too.

This will hopefully get rid of any spores from the algae and stop it spreading.

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Colin_T said:

Black beard algae is a pain in the butt. It leaves spores in the tank so even if you replace all the place, they just become infected again.

Some people claim a brand of plant fertiliser kills it but I can't remeber which brand they used. Personally I don't think there's a real cure for it and I tend to bleach plants and ornaments, flush the tank out, boil the gravel and start again.

Live plants can be put into straight bleach for a few minutes and then rinsed well under tap water. The bleach usually kills the algae on the plant but doesn't affect the plant if it's only for a couple of minutes (5 minutes in bleach is maximum).

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