R/O membrane

[ian cooper]

Hi all,

I think I need to replace the membrane in my Kent Hi-S unit. It is a 50 gallon/day unit, but I was wondering if I could replace the membrane with one rated at 25 gallon/day in order to save a little money. I don't need 50 gallons per day, only about 5 - 10 gallons. Just curious if it makes a difference as the membrane housing is the same size ( or at least appears to be the same size) for the 50 GPD as the 25 GPD. As well, what is the difference between say Kent Marine membrane, Coralife etc. and those manufactured by Dow. Are the membranes manufactured by the same company and just sold under different names? Any help would be appreciated. Thanks.
Ian

[ian cooper]

I should also add that I am not particularly concerned with limiting Silica in the make-up water as a recent article in Advanced Aquarist On-line Magazine indicates silica may be a limiting factor in the growth of sponges and other creatures in aquaria. Thanks.

[ajx22]

Any standard RO Membrane is able to be used - as long as you change the flow restrictor as well.

You are better off to purchase a 100GPD membrane as this will save you $$$$ over the long run. If you have a low-production membrane - such as a 25GPD - you are still running the same amount of water through the prefilters (sediment & carbon) but getting less RO water.

Say if you have a 100GPD RO unit and a 25GPD unit sitting next to each other. They are plumbed to the same water source and are both getting 65psi feed. In 24 hours, the 100GPD unit has produced 100Gal of filtered water, and the 25GPD unit has produced 25Gal of filtered water. In that 24 hours...the same amount of water has passed through both filters - thus using the same percentage of the life of the prefilters - but the 25GPD unit has wasted a ton more water with MUCH less produced filtered water.

If you consider that most RO filters make 1Gal of filtered water, for ever 4Gal of waste...and you consider that between the two above examples, there is a 75Gal difference in produced filtered water...then you can also imagine the amount of wasted water and the percentage of wasted prefilters. Your prefilters will actually exhaust faster in a lower GPD rated membrane system then with a higher rated membrane system. This happens because to get the same amount of RO water (say you need 5 gallons per day), you have used 4x the life of the prefilters with the 25GPD then with a 100GPD.

If you are trying to SAVE money...then you will want to purchase a larger GPD membrane - as you will be able to produce the needed 5-10Gallons of water in less time, thus using less water and less 'life' of the prefilters. I have a 200GPD RO/DI unit for the simple fact of saving money. I can run the unit for 20 minutes and get the 5 gallons of filtered water I need, and thus am making the unit so much more effecient.

If you price the Kent or other 'branded' membranes...they cost more then the Dow membranes - and the funny thing is that Dow likely makes the Kent/Spectrapure membrane too (as there are only two companies that manufacture RO membranes to my knowledge, and most all home RO filtration units use the Dow membrane).

If you price the Kent (or Spectrapure) 25GPD RO Membranes on-line - you are looking at between $100.00 and $120.00. If you check out our Dow membranes - you will see that they are only $100.00 for the 50GPD and $110.00 for the 100GPD. You will also notice that we do not carry the lower (below 50GPD) rated membranes - and this is the reason.

http://aquariumpros.ca/Merchant2/merchant.mvc?Screen=CTGY&Store_Code=A&Category_Code=RA

So to sum it up...it is backwards to try to save money by getting a lower production rate membrane.

I hope that this helps clear up some of the confusion here. Please feel free to call or e-mail us for more details and further explanations.

Best regards,

[ian cooper]

Thanks for the explanation A.J., I didn't think it through properly. I'll be in touch soon to order the membrane (after I pay for the car repairs @#%!!). Thanks, I appreciate the imput.

[ajx22]

No problem Ian...

I look forward to hearing from you.

Best regards always,