YamahaF934
Well-known member
Looking at Bulk Reef Supply, why do you need a 75 gallon a day filter when I am only changing 5 gallons a week???
Is there a reason or any other smaller ones.?
Is there a reason or any other smaller ones.?
RO Question
- Thread starter YamahaF934
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50 gpd and 75 gpd are pretty typical sizes. You don't need a 75 gallon per day, but you'll probably have trouble finding one smaller than 50 gpd.
Krish
RF STAFF
On a side note, make sure you are looking for an ro/di unit and not just an ro unit. I honestly can't remember why the ro alone isn't sufficient, but I do know ro/di is what you need. I'll search it a bit here to see if I can find the answer and if not, I'll start a thread on it to get some more info as to why. 
I've seen as low as 24GPD. Most (all?) RO\DI units you will find on reef supply sites use the same physically sized RO membrane (TW30-1812-xx Aquarium Water | Reverse Osmosis | RODI Water | ReefKeeper Water | Membrane). This means if you buy a 50GPD system you can replace the membrane with a 75GPD membrane down the road. The only differences I have found are that the 100GPD membrane has a lower rejection rate (90% vs 97%) and the 150GPD membrane requires higher input pressure.
It just depends on how fast you need to make water.
I started out with a 50GPD RO\DI MightyMite unit. I also didn't have room in the apartment where I could keep my water storage containers and RO\DI unit hooked on a float switch full time. Every weekend I would hook up my RO\DI unit in the bathroom and make 20 gallons of water. Half would go to the a water change and the other half was my top-off water for the week.
Making water on demand with the 50GPD was a painfully slow all day process for me. The water pressure in my apartment was a bit low to begin with and the system was MAYBE making 2 gallons an hour if I was lucky.
Slowly over the past few years I have been upgrading my RO system. First I bought a booster pump, then swapped the 50GPD membrane with a 150 GPD membrane. Finally I ordered a new 150 GPD RO\DI system from Bulk Reef Supply and attached my existing 150GPD membrane and booster pump. (I had to buy a new system vs just an additional membrane and housing because the mighty might came with small self contained carbon and DI filter canisters. I wanted the larger standard type with the replacable elements like you see on most systems.)
Even though I am no longer living in the apartment I still make water on demand. With dual 150gpd membranes and the booster pump making water is much less painful. One additional benefit is that running two membranes at higher pressure also results in less waste water. One drawback is that when I am careless epic floods also strike quicker.
So thats my justification of why someone might want a higher GPD unit. If I had my RO\DI unit hooked up and running full time a 50GPD system would probably serve my needs just fine.
It just depends on how fast you need to make water.
I started out with a 50GPD RO\DI MightyMite unit. I also didn't have room in the apartment where I could keep my water storage containers and RO\DI unit hooked on a float switch full time. Every weekend I would hook up my RO\DI unit in the bathroom and make 20 gallons of water. Half would go to the a water change and the other half was my top-off water for the week.
Making water on demand with the 50GPD was a painfully slow all day process for me. The water pressure in my apartment was a bit low to begin with and the system was MAYBE making 2 gallons an hour if I was lucky.
Slowly over the past few years I have been upgrading my RO system. First I bought a booster pump, then swapped the 50GPD membrane with a 150 GPD membrane. Finally I ordered a new 150 GPD RO\DI system from Bulk Reef Supply and attached my existing 150GPD membrane and booster pump. (I had to buy a new system vs just an additional membrane and housing because the mighty might came with small self contained carbon and DI filter canisters. I wanted the larger standard type with the replacable elements like you see on most systems.)
Even though I am no longer living in the apartment I still make water on demand. With dual 150gpd membranes and the booster pump making water is much less painful. One additional benefit is that running two membranes at higher pressure also results in less waste water. One drawback is that when I am careless epic floods also strike quicker.
So thats my justification of why someone might want a higher GPD unit. If I had my RO\DI unit hooked up and running full time a 50GPD system would probably serve my needs just fine.
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I had to come back and add a disclaimer. What I said above is what I believe to be true but there is one question that has always bothered me that I haven't been able to find the answer to. If there really is no difference between the 24, 50 and 75GPD membranes other than the GPD rating why sell anything other than 75GPD? Why would you ever want to make water slower? Do some retailers just offer systems with slower membranes just to upsell the 75GPD units and make a few more bucks? I've noticed the more reputable dealers offer smaller replacement membranes but always bundle the 75GPD membrane in their systems.
the6goat6man6
Well-known member
IMO, which probably don't mean much with little experience and I don't own one yet, But I think the idea is to try and keep a 50% water change on hand in case of an emergency. I try to keep 55gal of mixed salt water and 10 gal of fresh on hand at all times incase, well S#@& happens and it usually happens when you least expect it. So trying to be a good boyscout, try to be prepared! I have a 55gal tank I keep water mixed in, sitting on a dresser in my bed room. Not pretty but better than having a tank full of water sitting around my living room or something. I will be purchasing a RO/DI system soon, I am looking at 100GPD or larger with dual RO cartrages (just because i am parinoid). LOL
Does anyone know what the lowest pressure is to make good water without a pressure pump? I also am going to invest in a RO/DI system very soon but I have a well. We all know that the pressure with a well pump does go up and down when running. Sounds like it may not work without a pressure pump. Probably going to get a 100GPD.
the6goat6man6
Well-known member
Not too sure, i've read that they can work, but work better and faster with pump. not sure what gpd will work, may need to know actual water press. Easy, just put a water pressure gage under sink with "T".
NWDiver
Swimming with the fishes
If I remember right, I was told that 45lbs of pressure or more is good for the 100gpd filter that I have. I run at 50 most of the time.
also 75gpd membranes are rated that way at 60-100psi of water pressure and at 77 degree water passing through the membrane.
Most of our water is running way lower than 77 degrees witch will slow it down, and i m not familiar with seattle area water pressure but it may be lower than 60psi and if it is remember you will loose pressure going though the sediment filters and the carbon block. this will also slow a 75 gal per day unit down.
IMO: i have a 100gpd unit but only get about 30-35gal per day in with my current system.
IMPORTANT:
It was stated above that you can just change out membranes for more or less water but remember that for ever membrane there is flow restricting valve that needs to be replaced as well to keep the correct back pressure on the membrane to make it work properly.
Most of our water is running way lower than 77 degrees witch will slow it down, and i m not familiar with seattle area water pressure but it may be lower than 60psi and if it is remember you will loose pressure going though the sediment filters and the carbon block. this will also slow a 75 gal per day unit down.
IMO: i have a 100gpd unit but only get about 30-35gal per day in with my current system.
IMPORTANT:
It was stated above that you can just change out membranes for more or less water but remember that for ever membrane there is flow restricting valve that needs to be replaced as well to keep the correct back pressure on the membrane to make it work properly.
NWDiver
Swimming with the fishes
Good point Nate R. I think it takes my 100GPD pretty much 24 hours to refill the 55Gal. The water from the well is probably less than 40F and runs 50lbs.
the6goat6man6
Well-known member
check out one of the sponsers, airwaterice, i did earlier and they explain it
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