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My 20gal tank has at times a bad case of red algae forming on the sand.

I have done the following, done water changes, purchased Chaetomorpha Algae to combat the red algae and remove some red agae from the sand bottom. Today it really hasn't been that bad like the days before, so maybe it's working.

Anything else I can do?

Reduce your feedings, increasing the amount of time the lights are on and clean your filter media are some of the things I have heard.

What are you replacing the water with?

Hopefully it's being replaced with RO/DI water. 

I had the same problem in a 29 gal that I used to run. I found that I could reduce the phosphate and whatever else was changing my sand to have the redish pink color by doing 2 things. Reduce feedings, and when I thawed meat products I now always do it in a strainer either under running water or in a coffee cup. So the residual oils and stuff dont go into my tank. I found a couple of places online that recomended this, and it worked in my small tank. Give it a try because I notice changes in about 3 days.

PeterW:

What are you replacing the water with?

Hopefully it's being replaced with RO/DI water. 

 I have been using RO/DI water only and have done serveral water changes with RO/DI water. When I first setup the tank back in December I didn't have the RO/DI unit so I just used tap water. 

Castro:

I had the same problem in a 29 gal that I used to run. I found that I could reduce the phosphate and whatever else was changing my sand to have the redish pink color by doing 2 things. Reduce feedings, and when I thawed meat products I now always do it in a strainer either under running water or in a coffee cup. So the residual oils and stuff dont go into my tank. I found a couple of places online that recomended this, and it worked in my small tank. Give it a try because I notice changes in about 3 days.

Good tip Castro, thanks for posting it.