Zero Water

TDS is TDS...it's not like there's a specific reef measuring system vs a drinking water system. If you don't need to make much water, it might be a cost effective way to do it. When I just had my nano, I just bought Wal-Mart water which was under 10 TDS and only about .30 a gallon. Your LFS may have a good deal on water too, but nothing beats the convenience of being able to filter it yourself on demand.

--AJ

 

im curious about this, how much water is actually wasted with a ro unit? for instance i pay 2 bucks for 5gals of water not. outside of convience how cost effective is it to have my own ro unit?

 

If I remember correctly, you end up with about 25% of the water that you put thru the unit...so if you put in 100 gallons, 75 gallons are considered "waste" water and 25 gallons is your filtered end product. The actual cost of your filtered water depends on 1) how much your tap water costs you 2) how often you have to change your pre-filters, membrane and DI resin 3) temp of the water going into your RO/DI unit (room temp water is filtered at a higher efficiency than cold water and probably a few other factors that I can't think of right now. The way the same filter works for one person may be different than how it works for another person across town due to all of the listed factors.

--AJ

 

The only thing I would "caution" you about first is that you should remember that TDS is just a summation of effectively everything dissolved in your water. Generally speaking I wouldn't put too much thought to this, but it is worth noting that depending on what is actually left in the water, 2 TDS may not actually be "better" than a higher number of, say 5, TDS.

 

So Bela, to summarize what you said, if your 2 TDS is made up of a more harmful solid and your 5 TDS is made up of a more inate solid, then the 5 TDS water may actually be better water?  Just trying to make sure I understand what you're saying. 
If that's the case, based on the rejection rate of most membranes, wouldn't that mean that your tap water would have to have 20 times that level (assuming a 95% rejection rate...most membranes are rated at 98%, but don't perform at that rate with the cold water most of us use) of more harmful solid?  I would think that it would make that water harmful to us too, making the water fail the municipal water department regular testing...assuming of course that you're getting your water from a public water source and not a private well.
Assuming that your tap water is passing the regular testing of your water dept, then taking an additional 95% of the solids out of it, I would have to think that it would be safe for your reef tank no matter what the 5% solids are.
--AJ

 

Yeah, AJ. That is exactly right. Generally speaking, since we are talking potable water being de-ionized, we can assume a higher TDS is "worse" than a lower TDS. Mostly, it is the chlorine we have toworry about in regards to our fish tanks. The amount of chlorine in tap water doesn't harm humans, but if the chlorine is what is getting through and coming up on your TDS meter, that can cause issues for your tank inhabitants. FWIW calling it dissolved solids it a bit of a misnomer, really. It doesn't need to be a solid for it to be registered on your TDS meter.