Need RO Experts

[saltwater2642]

OK here it goes. The other day I tested my RO/DI water and found it was like 42 on the tds. So I think man gotta get my filters changed. So then I thought that the water was exposed to the air which it was and tested fresh water from the drip line. It tested at 0 so yea I capped the RO/DI container and filled the tank. Problem solved... right yea till I tell the wife and she asks this wife questions.

The capped 55 gallon contained has RO/DI water in it and as long as there is no air in it it will stay at 0 on the tds, Yes honey it will its ok I don't need the filters.

Well if thats true and you want true pure RO/DI water what happens to the water that's in the auto top off doesn't it get exposed to the air and absorb the minerals and things? And what about the tank water, the sump is open to the air and the tank is too. Well yes it is dear but.... I cant talk now I have to go do something.


So I ask you all why do we protect the RO/DI so much? We leave the tank and sump open.

[Randy Holmes-Farley]

The only thing in pure air that impacts TDS is carbon dioxide. It could raise TDS by 1 ppm TDS or so.

But if you have any salt spray in the air (like from a skimmer), then you could get salt into it. That will raise TDS a lot, but not be a problem.

None of these things are a concern for using the water. TDS is not to be used to indicate water is bad, but rather an indication of whether the RO/DI is working properly.

Tank water has a TDS of many tens of thousands of ppm TDS, and it is fine. RO/DI passed over a brass part might have 1 ppm TDS and kill everything.

So just use it to determine when to change the filters, and let the RO/DI worry about removing what is bad.

This article has more:

Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria
http://reefkeeping.com/issues/2005-05/rhf/index.htm

and

What is TDS?
http://www.reefkeeping.com/issues/20...ture/index.php

rom the first one:



If you are evaluating an existing RO membrane and can collect water from the tap and after the RO membrane, the conductivity (in mS/cm or ppm TDS) should drop by a factor of more than 10 across it (to as much as 100), relative to the tap’s water. If the drop is less than a factor of 10, it is not working properly, and may have holes in it.

Monitor the DI resins by measuring the effluent’s conductivity, either with an inline meter (set to its most sensitive level), or by measuring the effluent manually. If you are using a TDS or conductivity meter, then the measured value should drop to near zero, or maybe 0-1 ppm TDS or 0-1 mS/cm. Higher values indicate that something is not functioning properly, or that the DI resin is becoming saturated and needs replacement. That does not necessarily mean, however, that 2 ppm TDS water is not OK to use. But beware that the flow of impurities and the conductivity may begin to rise fairly sharply when the resin becomes saturated. Do not agonize over 1 ppm versus zero ppm. While pure water has a TDS well below 1 ppm, uncertainties from carbon dioxide in the air (which gets into the water and ionizes to provide some conductivity; about 0.7 mS/cm for saturation with normal levels of CO2, possibly higher indoors) and the conductivity/TDS meter itself may yield results of 1 or 2 ppm even from totally pure water by not being exactly zeroed properly. Also note that the first impurities to leave the DI resin as it becomes saturated may be things that you are particularly concerned with (such as ammonia if your water supply uses chloramine or silica if there is a lot in the source water).

[saltwater2642]

Thanks this helps a lot.

[Randy Holmes-Farley]

You're welcome.

Happy Reefing.