Need help choosing RO unit

[FortuneFavours]

Hi all

What size (in terms of production capacity) RO unit do I need for a 300G reef tank?
How many stages should I be looking for?
Is DI required/beneficial?

I'm aware that I won't be getting anywhere near the advertised GPD and that I'll need good water pressure (or a pump if water pressure is poor).

Any info on the estimated amount of top up water I'll need will be useful (tank will be covered, size is 60" x 30"W x 40"H). Also, what sort of water change schedule should I be looking at?

Many thanks!!

[James77]

Actually, the GPD rating is pretty accurate....it all depends on your water pressure and temperature. I have a 75 GPD membrane, and my water pressure is 60 PSI. In all but the winter, it is more like 90 GPD. A 75 GPD membrane is the most efficient in terms of rejection, meaning it rejects the most.

4-5 stage is enough. You would want 1 or 2 sediment blocks, a high quality carbon block, the membrane, and the DI. DI is very beneficial, as it will remove TDS your membrane missed.

You should not really need more than 75 GPD. Aside form the initial fill, chances are you will never use that much water at one time. Top off varies greatly. Being covered will greatly minimized evaporation. But temperature difference between the ambient room and tank matters. My 120g covered loses maybe 1/2 to 3/4 a gallon per day. An old uncovered 175g with basement sump I had would evaporate 5-6 gallons a day since it was an open sump in a very cool cellar.

Water changes.....20-30% a month, either all at once or several times is fine.

[phillrodrigo]

The spectrapure refurb units are great. IT's the one I have and other than the carbon and sediment the filters lasted over a year the original ro is still there after 2 years

[FortuneFavours]

Originally Posted by James77

Actually, the GPD rating is pretty accurate....it all depends on your water pressure and temperature. I have a 75 GPD membrane, and my water pressure is 60 PSI. In all but the winter, it is more like 90 GPD. A 75 GPD membrane is the most efficient in terms of rejection, meaning it rejects the most.

4-5 stage is enough. You would want 1 or 2 sediment blocks, a high quality carbon block, the membrane, and the DI. DI is very beneficial, as it will remove TDS your membrane missed.

You should not really need more than 75 GPD. Aside form the initial fill, chances are you will never use that much water at one time. Top off varies greatly. Being covered will greatly minimized evaporation. But temperature difference between the ambient room and tank matters. My 120g covered loses maybe 1/2 to 3/4 a gallon per day. An old uncovered 175g with basement sump I had would evaporate 5-6 gallons a day since it was an open sump in a very cool cellar.

Water changes.....20-30% a month, either all at once or several times is fine.

Thanks James, that's really helpful. I found a decent 4 stage 100GPD unit which I'm hoping will do the trick. The RO unit will be housed outdoors (albeit in an insulated box I'll be building for it), so I think performance will drop a bit.

The info on the evaporation is super helpful! Thanks.

Originally Posted by phillrodrigo

The spectrapure refurb units are great. IT's the one I have and other than the carbon and sediment the filters lasted over a year the original ro is still there after 2 years

I had a quick Google and couldn't see that for sale in the UK, so hoping the model I found will work.