Originally Posted by
jeep
I just helped a friend install that same unit last week. He did buy the additional DI add-on because he plans to use it for salt water in the future. Very nice!
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DI is not required for discus. Even RO is overkill in most cases unless you are breeding or have a terrible tap water source. Even then, RO is only needed at the time fertilization takes place. If using RO, you should also re-mineralize the water. There are mineral recipes here on the forum, or you can just use the RO waste water to achieve your goal.
The DI process just cleans the remaining compounds that RO doesn't filter out. It takes your +-18 TDS down to 0 TDS. It passes through a resin that must be replaced or recharged once the resin is exhausted or else it will bleed undesirable compounds back into the water and it will smell like rotten eggs. It's the closest thing to distilled water you can produce. It also has no buffering ability, as does pure RO, so a ph crash becomes an issue. Also, discus need the trace minerals in regular or re-mineralized water. Especially fry!
Unless your tap water source is bad or you're breeding, most tap water supplies are fine for discus. When I make RO water, I save the waste water for remineralization or for all tanks other than breeders.