Brown algae doesnt mean your fish are sick hun.
Brown is due to Phosphates in the tank, or high amounts of nitrates, or not enough light.....
Green algea pea soup we like to call it is cause by to much sunlight geting in the tank....
Brown algae can be cured,,
1. Rubbernose or BushyNose Pleco.
2 more water changes.
3. cleaner filters or higher filration rate.
4. less food fed to the fish.
5. Phossorb that can be added to the filter.
Its not bad to have just more of an annoyance

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DO NOT use sick fish as water will turn brown instead. If fishes fall sick in between, water will turn brown too. You can add a small clip fan (cheap) to blow away the heat generated from the light, as I have done. Feed the fishes with HIKARI sink pellets to build up ammonia level to kick start the algae.