Ro unit

Probably would be better to use it for African cichlids. It maybe too hard. Test it before trying.

 

I'd only add that your choice of a 75gpd model was a very good one...it should get you "good" production (in painfully slow ro/di water-making terms, of course). "5-stage" sounds like overkill. Mine's plumbed to my hot water line in my laundry room...that will also help you pick up a pace somewhat.

 

one other thought, do you have a pressure gauge on it? Most units will require a min of 40psi but run much more efficient with 60-70psi from the supply line. it might be beneficial to add a booster pump if it's too low.

 

Never, never ever, did I say never, hook an RO to a hot water line! That is the fastest way to ruin a membrane there is. RO membranes cannot take anything over 113 degrees F and will literally melt.
Always use cold water and boost the pressure if the production rate is not enough for you. Pressure will overcome the effects of cold water and give you better product or treated water quality since membranes work better with cold water since it is more dense.

Don't get hung up on "Stages", it really doesn't mean anything. Its what each stage contains that is important not how many. For RO you want and need 3 "stages" and for RO/DI you need 4, thats it.

Dow Filmtec rates their membranes at 77 degrees F water temp and 50 psi available at the membrane as well as 250 ppm TDS softened water and 85% recovery, any deviation from these and it either lowers or raises the production and water quality.

Average water pressure across the country is probably close to the 50 psi, the nationwide TDS is about 250 but the temperature varies greatly. Most RO and RO/DI units are supplied with a fixed type flow restrictor which is probably close to 4:1 but is not precise. I would suggest EVERYONE test their waste ratio and get it as close to 4:1 as they can either with an adjustable flow restrictor or better yet a capillary tube flow restrictor you trim for your exact water conditions, this one step makes a huge difference in production, water quality and membrane life.