Does it have to be 0 TDS?

yeah he will, and he's right, but i'm ok with a hint

 

Mine is 0 typically...once it starts to go up to 1,2,3,4....I order new filters etc and change them out....I dont freak out about it though....I am happy to use the 1-5 RO/DI water in my tank while I wait on new filters...has had no negative impact that I can see.

 

Funny that people say you need 0. I guess we were all a bunch of failures when we used RO only. What about those who used Kold-Steril units back then. Those didn't even have a membrane. Wow ho times have changed.

My TDS is 40 because I use a 100gpd membrane with approx 90% - 93% rejection rate. Yep my tap water s over 500 tds coming out of the membrane. No I'm not saying that you should do what I do, but what I am saying is that it does not have to be absolutely zero.

If you buy purified fresh water, it's not 0. If you buy water from the fish store, its not zero. If you buy salt water from the fish store it did not start with 0 either. Wholesalers aren't using 0 TDS water to make salt water either. Less than 5 TDS is great, Less than 10 TDS is very good, Less than 20 TDS is still on the good side.

 

I will say that my 50GPD RO/DI unit consistently puts out "0" water...it only goes above 0 when it is ready for filter replacement. I just have the basic air/water/ice Typhoon 3. Relatively low cost, and it performs well. My tap is no where near 500 though...it is like 140...

 

yuppppp

 

a 50 gpd membrane has a 97-98% rejection rate so before DI you should be down around 4-6. DI will then take that down to 0. When my Tap water was 140 10 years ago (prior to urban sprawl), my water was always 0. I can get it down significantly if I change the membrane to 75gpd as they have 95-97% rejection rate. I already have it but since I will soon be taking down the tank, I will wait to change it when making water for the new tank. Hopefully my new city will have lower TDS!

 

the RODI water that my LFS sells and uses is anywhere from 8 - 16, and they run a pretty successful business with it. i change my filters out when it gets to 2, but itll go from 0-5 withing a few days, so once it starts gettin bad, itll get bad realy quick.

 

Ideally it should be 0 TDS. The problem is since TDS is not a measurement of anything specific, you have no idea what that 4-5 TDS is. It could very well be nitrates, phosphates or silicates. RO membranes are not particularlly good at removing some things as is DI resin with weakly ionized substances like the three above. You cannot accurately test these in high purity water either so spend some money and upgrade your system or cartridges so it can at least get you started at 0 TDS. It may nnot stay at 0 TDS for long though as this is where better "reef specific" RO/DI systems shine and are worth the extrat couple bucks they cost. I change my DI when I first start seeing anything other than 0 TDS myself.

 

Thank you for the comment AZ. Is this non-zero TDS actually proven to be the problem for some tanks? or is it just a precaution? I have been trying to find if there is any issue with people's tank without 0 TDS. But I have found some people success with tap water.

 

When the SW hobby first started, it was a common belief that water was water. Period. We had no type of filtration for tap water. Yes, there were plenty of successful tanks, but there were also numerous utter failures along with the majority which were systems that were terminally problematic. As AZDesertRat already stated, the problem with non-zero TDS is that you don't know what contaminants you're dealing with. If it's nutrients, you'll constantly be plagued with algae; if it's heavy metals, a lot of sensitive life forms may be short-lived. While it's possible that your 4 - 5 TDS is mostly harmless, zero TDS removes the question mark concerning water quality should you ever encounter any problems.