RO/DI water is almost pure and has several uses in fishkeeping especially in marine aquariums. In freshwater aquariums, RO/DI water can be used routinely in auto-top-offs to prevent GH/KH accumulating when topping up due to evaporation. Carefully mixing London tap water with RO/DI reduces water hardness to better replicate some conditions found in the wild. This is especially important to encourage natural behaviours of many of the fish species we keep and increase spawning rates.
A downside to using RO/DI is the wastewater produced by the process. For every 1L of pure water produced, around 3L of high TDS water is “wasted”. Most places I’ve seen including our research labs simply dispose of the waste water down the drain, but at home this water can still be used for anything that doesn’t require low TDS like cleaning or watering plants.
Anyway, now that it’s set up I wonder why I didn’t have this before. It’s so convenient compared to carrying barrels of water from the aquarium shop (or from work ) and super easy to get going. You can plumb it into your main water line with a self piercing saddle valve, or attach to an outside hose tap like I did.
I bought mine from Vyair (UK) and they were super helpful in advising me on how to set up my unit. Mine is the RO-100M, currently using without a resin stage as I don’t need ultra pure water, but nice to have the option in case my needs change.
ATR93 