RO membrane TDS

[discuspro]

What should a normal TFC RO membrane have as a TDS reading when it is working properly?

[hammondegge]

in Austin, about 15ppm after the RO and 0 after the DI. I believe it is about 145 untreated.

[Ross]

Austin water is good compared to san antonio. Our tap water at Fin-Addict is like 320.

[hammondegge]

you guys suck it straight from the ground dont you? might just be some good hard aquifer water.

[discuspro]

Okay, I've got 0-1 after DI but I'm going to double check after my RO membrane, I checked today really quick and it looked a little high.

By the way, where do you guys get your carbon filters and prefilters from?

[hammondegge]

i like these guys
http://www.buckeyefieldsupply.com/

[discuspro]

I'll have to consider them, looks like good stuff.

Anyone buy their carbon and pre filters in Austin, like Homedepot or Lowe's or something?

[discuspro]

Okay Chem analyists, here we go! After taking water directly after the RO membrane(fresh) I got a TDS reading of 25 and pH of 9.04; the reading was taken while being stirred vigorously. I might get a different reading when the water has been aerated but I'm not sure if it is aerated or not to begin with after it comes out of the RO membrane.

Then straight out of my DI after my RO membrane I get a TDS of 0 and pH of 4.74, again not yet aerated but stirred vigourously while testing.

Does that sound right or is my RO membrane shot? Also would it help if I left the water out to equalize gas levels and then take another reading?

[JimD]

Tell me what your tap water tds is and Ill let you know the efficiancy of your membrane. Make sure you put the samples in a fresh sandwich bag and not a used container of any kind, this will greatly affect the readings.

[astrong]

Yeah that sounds right. The TDS should be higher from the RO and then the DI will filter more impurities out, mostly charged particles. pH is unimportant. pH will be affected by CO2, O2, Ammonia, how recently you calibrated, etc. RO/DI and RO will adopt whatever pH you put it into because it has no buffering capabilities, which is one of the reasons we like it!

[discuspro]

Jim I'll get you my tap TDS by tomorrow.

I would think even though there is, theoretically, little or no buffering capacity in the water after the RO it would tend towards a pH of 7 once the gas levels have equalized :huh. If the TDS is low wouldn't that mean the more pure the water would be? Also, is there normally any ions or molecules that pass through an RO membrane and must be taken out by DI?

I'll just let some sit out for a day or so or mix it up for a day or so to get the gas levels equalized in both water coming out or the DI and RO membrane.

All of this stuff is all an attempt to try and zero out nutrient sources giving my cyano a 7 course meal.