RO/DI question, need something explained please

[Brian_R]

I asked this question on a different board as well, but thinking back on it, I trust the information I receive here more then anyplace else so reposting this here.

I am setting up my new 75 gallon tank. I am purchasing an RO/DI unit of course. I was going to email FilterDirect and see if he could build me a 75 gallon unit rather then buy one of his 100 or 110 units off EBAY. The reason? Because I had always heard that the 75 or less RO/DI units would clean your water much much better. Is that only true though if you just purchased an RO unit? Would purchasing a RO/DI unit still get your water just as clean no matter what? Perhaps with a 100 or 110 unit you might have to change out the UI resen more often? Or should I still follow my original plan and see if FilterDirect can build the 75 gallon unit? Is the reason the 100 and 110 units are so cheap is because of the fact that the 75 units parts cost more to make?

Brian

[SPC]

Hi Brian,

Originally Posted by Brian_R

I had always heard that the 75 or less RO/DI units would clean your water much much better.

No this shouldn't be true, and if it is for some reason that I am not aware of, I don't think the difference would amount to a hill of beans.

Would purchasing a RO/DI unit still get your water just as clean no matter what?

Yes, if you are comparing apples to apples.

Perhaps with a 100 or 110 unit you might have to change out the UI resen more often?

If you run 50 gallons through the 75 GPD unit, and 50 through the 100 GPD unit, your DI should be at the same level of exhaustion.

Or should I still follow my original plan and see if FilterDirect can build the 75 gallon unit?

I would check with Aqua FX and Aquatic Reef Systems before I made my final decision. I have no expereice dealing with FilterDirect but have dealt with these other two for years and know that they have excellent customer service.

Is the reason the 100 and 110 units are so cheap is because of the fact that the 75 units parts cost more to make?

Good question, it may be just a volume thing.

Steve

[Clownfishman]

I purchased one of the 100 GPD units off of ebay for $69 you just can't beat that price... I think reefboydc has one to and recommended them... said he had one for a year or someone here on the board did..

[Doug1]

As I understand it the main difference in Ro units is the amount of water they are reated to process in a 24 period. Notice that there are limits to the starting turbidity, water pressure and temperature to run at maximum efficiency.
There will always be some stuff that passes thru the osmotic membrane and thats the function of the de ionizing resin's function to remove that.
The more efficient the prefilter stage, the better service you will get from your RO setup
My dream water processing setup would be a carbon filter-5 micron sediment filter-poly filter(like Kold Steril) then RO membrane to DI filter, at 70 psi and 70 deg F

[Doug1]

As I understand it the main difference in Ro units is the amount of water they are reated to process in a 24 period. Notice that there are limits to the starting turbidity, water pressure and temperature to run at maximum efficiency.
There will always be some stuff that passes thru the osmotic membrane and thats the function of the de ionizing resin's function to remove that.
The more efficient the prefilter stage, the better service you will get from your RO setup
My dream water processing setup would be a carbon filter-5 micron sediment filter-
BTW and FWIW there are only a couple of producers of Reverse Osmosis membranes so everyone making RO setups uses one of 2 or 3 mfgr units, it's all about the prefilters and such, thats what they are refering to when they say Unit so and so is a X stage unit,
barebones unit is usually a combined carbon/5 micron prefilter and the RO membrane, the fancier units have separate carbon and sediment filters, often a large(5mic) and a small(<1) and of course the DI cartridge(se) count as a stage

[Doug1]

Addendum, I know that doesn't answer the question directly, and I am not going to recommend a specific brand, but you should know that the membranes are all very similar, what you are paying for is the number and quality of the pre and post filter stages, ie filter housings etc. Clear housings usually cost more than opaque.
The prefilters inserts are cheap and should be replaced frequently, esp if you have chlorinated water and or a high Total disolved solids level, lots of rust or other particulates.
A back flushing feature is a good investment and a TDS meter is pretty much a must, you will want to monitor TDS in and on the final output side to check on the efficiency of the unit.