Hello and thank you for your inquiry.
Red slime or cyanobacteria is usually caused by one or a combination of factors including flow (lack of), water quality (nitrate and/or phosphates) and/or old lights.
To help combat red slime one of the best solutions I have found includes the following:
1) Increased water changes, making sure to use filtered water (RO or RO/DI) mixed with a high quality salt. During the water changes you will want to siphon out as much red slime as you can. I will try to do 20-30% water changes every 2-4 days.
2) Decrease the amount of time the lights are on, even keeping the tank dark for a couple of days. If the bulbs are older I recommend changing them out, but slowly ramp up how long they are on for. New bulbs can also cause an outbreak if the red slime is already there.
3) Decrease the amount of food being fed. Less food in generally means less waste being produced.
4) Increase water flow within the tank trying to eliminate any dead spots within the tank.
5) Using some type of phosphate removing media (like Phosban or Rowaphos) to aide in the removal of phosphates from the water.
While I personally have never used any type of red slime removing medications, so people have used them with sucess so that may be an option for you as well.
Below is a link about getting rid of Nuisance Algae that might help as well:
If there is anything else we can do for you please let us know.
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