I'm trying to cut back on water changes. I currently do a 20-25% change once a week in my 55gal ciclid tank. I don't use carbon because disposble doesn't work for me. I'm currently using Seachem's Purigen as my chemical media. Of the others on the market that can be regenerated and used indefinitely (API Nitri-zorb, Fluval nitrate remover, etc), which is most effective?