what to do

some people told me that i shouldn't run a hang on filter just my skimmer and liverocks. could this be the problem? i removed my sponge but left the carbon in. do you use a water conditioner when using ro water?

 

I don't use a water conditioner, but I still use carbon and phosphate sponge. Also, I don't think there's anything wrong with the hang on back filter as long as your not sucking anything up with it like anemones and snails etc.

 

I'm curious how often you replace your phosphate sponge. How many times do you bake it before replacement?

 

It is best to use a little phosphate remover as well as carbon for that matter and replace it every couple of weeks or so. Alot has to do with bioload as well, but usually every 2-3 weeks is best and replace it.
Water conditioner is not needed with RO water since their is no chlorine, or chloramine in the water.
As for the hang on filter goes, I use one on my 30 hex which offers me the option of adding phosphate remover or carbon to my water by dropping it in the filter. Moreover, it offers you another form of water flow!