RODI unit low vs high GPD?

LordDarth Bane

New member
So I am looking for a RODI unit for my 100G SPS system. The TDS of my tap water is 117ppm.

The place I intend to put the unit has no socket nearby so I want an unit that doesn't need electricity (no booster pump).

So, questions:

1. Is GDP high better than low?

I have checked out many units with GPD from 50G to above 400G. Most branded one such as Kent, BRS, Spectrapure and Vertex are from 50G to 200G. But those cheaper "ebay type" have 400G or even 800G.

They all "claimed" no booster pump is needed. But do the higher GPD one needs higher pressure to work? In theory a higher GPD membrane has bigger surface area which allows more "pure water" to pass through.

I am confused and I have asked several sellers:

A only has 125G. He said those 400G without booster pump are "low pressure membrane".

B sells units from 50G to 400G. He suggested only to use 50G without booster pump. (The higher one like 100G may not work without booster pump).

C sells both 125G and 400G. He said both don't need booster pump and the 400G could produce more water than the 125G.

D sells 100G to 400G. He said 400G needs much higher pressure to work.

.......I am confused. So what is true?

Is it higher GPD needs higher pressure to work?

And for those high GPD membranes that work with low pressure (low pressure membrane), their rejection rate is low? (which means the output TDS is higher?)


I am just curious, why some cheaper units have much higher GPD like 400G but our branded aquarium used ones are usually only around 50G~100G?

So for a unit without booster pump, what GPD shoud I choose?

Thoughts?

Thank you.
 
A standard 75GPD system will likely be just fine for you..
You will only need to make that much when filling up the tank.. It will take 2 days to fill your tank initially..

But..
What is your current homes water pressure? I would suggest going to the hardware/home improvement store and buying one that attaches to your outside spigot or whatever so you can see what it is before you purchase just incase you need to get a booster pump.. They are like $10 or so..
Or just wait and adjust as needed and get a system that comes with a pressure gauge..

If its not 50PSI or greater you will need to adjust it so it is or get a booster pump.. (I just suggest adjusting the water pressure regulator if you have one as you will probably enjoy the higher pressure for showers/washing dishes,etc...). I set mine to 60 PSI by simply turning a screw (bolt actually)

All the membranes have a rejection percentage based on "X" PSI.. You need to come close to meeting or exceed that some to get rejection rate or its not running as efficiently as it could..

There is no need to get anything more than a 150GPD system for you IMO..

Where are you located?
 
I agree with mcgyvr. A pressure test will tell you if you need to either adjust your regulator or use a booster pump. My pressure was about 45 psi, but I adjusted it to 60 with the regulator which is what my unit needs without a pump. You should not use a unit with less pressure than it requires for efficiency.
 
Membrane production is based on a pressure rating AND a temperature rating by every manufacturer. Not reaching these parameters will definitely affect the way the unit performs.
 
I agree. Testing your pressure is the first step to determine if you can get away without a booster pump. At my old house I had 65 psi from the mains. At my new house it is closer to 95 psi.

Note, that the rated output is based on both temperature and PSI. The temperature they use for rating is impractical in real life (do NOT use your hotwater feed), but you can still achieve the stated rating by using higher pressure. They test at 60 PSI (if I remember correctly). My 95 PSI is probably too high, but my RODI shows 80 PSI on the gauge while it is active.

Dennis
 
Thanks. I haven't checked but I think the pressure is enough as the tap isn't slow.

Another question:

Should I get an unit with 3 or 4 canisters? I read that there are different "recipes".

5um or 1um sediment filter > carbon block > RO > DI

or

5um > 1um > carbon > RO > DI

or

1um > carbon > carbon > RO > DI

or

1um > carbon > RO > DI > DI........


Would an additional canister reduce the water pressure going into the RO?
 
The reason for running these diffrent setups is based on the water qulaity. Some people require more depending on their water quality. Sediment filters remove particals out of the water. Carbon filters remove chlorine and the di resin polishes up whatever is left that the membrane let pass through. For example, you don't want chlorine getting to your ro membrane, so if you water has high chlorine it would be benifical to run 2 carbon blocks to make sure it doesn't.
 
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