I know the best way to test the water is by a tds meter but i dont know anyone who has one and cannot afford one. I am out of the hobby but was contemplating coming back since i have a 2.5g aio built with all equipment minus an ato. I only used the coralife 24gpd ro di unit for maybe 3 months and probably made 50 gallons of water with it previously. when i took down my 30 gal breeder i put it away in storage. There was a little water in it. Do you think the membranes are still good or should i replace them...any ideas without using a tds meter? Thank you- Andrew

PM AZDesertRat, he's pretty wise about RO/DI. I'm pretty sure that if your membrane dried out, that's a bad thing.

Yea, I improperly disconnected my RO/DI and just left it like that for 3 months, and when our water filter changer guy came by, he took a look at my unit too and said it's better to just throw it away and buy a new one. Something about bacteria grown too.

If the membrane was allowed to dry out its more than likely shot. Only a TDS meter will tell, theres nothing visible you can see.

TDS meters are cheaper than the cheapest refractometers, just sayin'....

Thanks for the responses I really appreciate it.Basically reinforces what I believed. The membranes were not dried out they were kept with water in them, not sure if that makes a difference. I guess only a tds meter can tell... o well






...I know that, but being a college student who is independent and pays for everything on a low salary makes buying a tds meter a little more complex. I was just trying to get some input on a topic that i have not seen much about. I know this is not a cheap hobby (especially if you plan on doing things right) and hence why i do not have a tank right now. One can dream right?

my ro/di unit sat in storage for over a year and upon firing it up again a few month ago it works fine. confirmed w/ a tds meter.

by the way...you can buy a descent tds meter for about $15-20 at fred meyers/krogers on the brita water filter aisle in the kitchen section.

Sounds good lgreen, I will have to check that out next time I am at the grocery store.

Make sure you test the RO only not just the RO/DI. DI can make any water 0 TDS for a very short time. The RO membrane is the workhorse though and needs to be in the 95% range or DI won't last worth a hoot.

i didn't even think of that. i'll have to check my ro!

Many people neglect to test their RO only TDS and assume everything is as it should be when they see a low final TDS number. The RO membrane is the most important part of the process though and needs to be in top condition or the DI resin then becomes the "Crutch" holding it all together. DI resin can get pretty expensive when it if forced to clean up things the membran was intended for.
Just because you are getting low or even 0 TDS does not mean the system is working well, check that RO only TDS to make sure the membrane is working. At $35-$45 for a new membrane you can save a bunch on DI replacements over the next 3 years or so.

dubsmcfly, there is only one membrane. Its in the fatter horizontal white housing, the others are prefilters, carbons or DI. The two that must remain wetted are the RO membrane, which you cannot se if its wet or not unless you unscrew the end of the housing, and the DI resin which loses its electrical properties when it dries out.

Thank you for all the information, and I mean it... I learned more in that post then I did in my hour and a half econ class today hahaha. I guess you are the water guru!

Aw shucks!
Thanks, I'm just here to help like others have done for me.