Brown Algae (Diatoms)
Diatoms most commonly appear as small soft clumps of brown or yellowish green particles, in patches or as a stringy brown mass. It is extremely common in new aquariums that are still cycling but can also appear in tanks using a DIY dirted substrate or those with low plant mass.
It can also appear if your filter is unable to provide a sufficient amount of filtration and beneficial bacteria for your bio-load.
Most of the time with diatoms, it’s simply a case of waiting for your aquarium to mature. You can siphon or otherwise manually remove visible diatoms but they will quickly reappear. Once your cycle has established, diatoms will rapidly dwindle. For faster results, you can use commercially available products to help speed up the cycling process.
If you’re using a DIY dirted substrate, it might be leeching ammonia into your water column, which can also cause diatoms to appear. Check that you have a sufficient “cap” over the dirted portion of your substrate and increase its depth if not. Try not to disturb your substrate while planting as this will also release ammonia.
As always, increasing the amount of plants in your aquarium or encouraging healthy plant growth is always beneficial, both in reducing algae and for the overall health of your aquarium system.
There are plenty of livestock options that will eat diatoms – snails, shrimp, otocinclus and more. Apart from previous suggestions, if your tank is cycled and can support them, consider adding a crew of algae eaters!