Biofilm, mulm and debris: what should stay in a shrimp tank?

Preserve useful grazing surfaces, but remove decaying food, disintegrating leaves and accumulation obstructing flow. There is no visible dividing line where a coating is always “good biofilm” or “dangerous dirt”. Assess the material, aquarium function and measurements together.

Three terms with overlapping contents

Biofilm is a surface community that can include algae. Keepers use mulm for loose deposited material including decomposing residues and microorganisms. Material called dirt can therefore contain living organisms. Their presence does not make every heap suitable food.

Neocaridina can graze colonised surfaces. The biofilm experiment supports their value under its conditions, not unlimited accumulation or complete nutrition in every aquarium. See biofilm as food.

Choose the intervention by function

• Thin growth on accessible wood or a rear pane: some may remain where animals and water quality are normal. Clean viewing areas as needed.
• Leftover food or substantial dying foliage: remove it and investigate why it accumulates.
• Deposits around an intake, moss centre or feeding place: selectively clear the passage and check restored circulation.
• Deaths, abnormal behaviour or detected ammonia/nitrite: promptly follow the health route. Do not wait for the substrate to look “dirty enough”.

Smell, dark colour or bubbles may justify investigation, but do not measure oxygen or prove a specific substrate toxin. Do not churn the whole substrate to test that idea. Use targeted siphoning and check removed water for juveniles.

Sources and scope

• UF/IFAS: Cherry shrimp, Neocaridina davidi
• Viau et al. (2020): Neocaridina davidi in a biofilm-based culture system
• UF/IFAS: Dissolved Oxygen for Fish Production
• UF/IFAS: Ammonia in Aquatic Systems

Grazing and biofilm are described for Neocaridina; decomposition and nitrogen processing come from general aquaculture guidance. Maintenance choices are editorial. Colour or smell cannot establish safe oxygen, complete nutrition or a particular poisoning.