Red Slime Algae on Sand bed Need Help

TysFish

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Hey everyone,

I’m looking for some advice on this rust-colored algae growing on my sand bed. It looks like a slimy layer and tends to sit mostly on the sand rather than the rocks.

I do know a CC would help but the tank has a mantis shrimp and I know they wouldn’t last long so I’m trying my best to not get a CC.

Parameters 3 days ago:
• Nitrates: 0 ppm
• Phosphates: 0.2 ppm

I started dosing nitrate at about 1 ppm per day.

Parameters now:
• Nitrates: ~3 ppm
• Phosphates: ~0.1 ppm
• Calcium: 460 ppm

It seems like phosphate dropped slightly after nitrate became detectable.

Does this look like cyanobacteria, or could it be something else?
Any tips on the best way to handle it?

Tank is a 40 breeder, recently reworked the rockscape as well if that matters.

Here’s a photo

20260220_135338_DAA94C12-0846-4B58-BDDE-8618C5B2C5F3.png
 

Marine Betta

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Hey everyone,

I’m looking for some advice on this rust-colored algae growing on my sand bed. It looks like a slimy layer and tends to sit mostly on the sand rather than the rocks.

I do know a CC would help but the tank has a mantis shrimp and I know they wouldn’t last long so I’m trying my best to not get a CC.

Parameters 3 days ago:
• Nitrates: 0 ppm
• Phosphates: 0.2 ppm

I started dosing nitrate at about 1 ppm per day.

Parameters now:
• Nitrates: ~3 ppm
• Phosphates: ~0.1 ppm
• Calcium: 460 ppm

It seems like phosphate dropped slightly after nitrate became detectable.

Does this look like cyanobacteria, or could it be something else?
Any tips on the best way to handle it?

Tank is a 40 breeder, recently reworked the rockscape as well if that matters.

Here’s a photo

20260220_135338_DAA94C12-0846-4B58-BDDE-8618C5B2C5F3.png
Do you see any bubbles on the “algae”. How old is the system, and did you use dry or natural live rock? It looks like dinoflagellates or Cyanobacteria. Given that your nitrates are so low, I would think it’s dino. If there are bubbles on the mat, it’s probably dino. The simplest solution is increasing nutrients which you are already doing. Some other easy options to use in tandem with increasing nutrients include a UV sterilizer, siphoning off the mat (which is temporary), and dose some beneficial bacteria. If none of these work, blackout the tank for 3 days. If that still doesn’t work, try using dinox.
 

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