The strive for 0 ppm tds

[Cliff Puckstable]

I've been talking to some people on this subject. Why do we have to have 0 tds? Have you seen your mixing bucket lately? What happens to 0 ppm rodi water when it hits that bucket than add salt? Will >50ppm make that much of a difference when going into your tank? I can't remember the last time I changed my filters. I know for a fact I've never changed my membranes. 

[Brian Ward]

Yes it makes a difference. There have been a couple of posts. This one is probably best for you:

http://wamas.org/forums/topic/50900-cheap-source-of-di-resin/?do=findComment&comment=427458

 

But basically, once the DI resin is depleted it begins releasing the ions with the lowest charge which are actually the worst ones for your aquarium.

[Jason Rhoads]

I have good results using my 160-200tds tap water for water changes.  

 

I do get some algae, but who doesn't, and why is that necessarily a bad thing?

[surf&turf]

100 tds tap water here.

[s2nhle]

Maybe this article will provide some answers.

 

http://www.healthguidance.org/entry/14913/1/What-Chemicals-Are-in-Tap-Water.html

[zygote2k]

I have a few tapwater reef tanks and one of them has a Duncan with 2" heads. Apparently it's fluorishing. I don't even worry about the TDS in these tanks.

They don't get dosed with anything other than Prime to dechlorinate the water.

[Cliff Puckstable]

I love it. I think the whole 0 tds is a scam. But that's just me.

[surf&turf]

I must confess that our tap water comes from a spring here in Capon Bridge, but its still city water. 

[Origami]

0 TDS gives you a baseline of understanding of the ions in the water. That is, practically speaking, zero. This means that, when you mix up a batch of saltwater, that you get consistency in the results (so long as the manufacturer is remaining consistent.

 

For example, mix up a batch of IO or RC and you'll get a consistent level of calcium in the water that you can depend on. Mix it up with tap water, and it'll be elevated and the degree of elevation will depend on the hardness of the water in your area or municipality, or water conditioning system in your home. There will also be other ions in the water that vary over the course of the year. Some you don't care about, others you may care about. If they're not part of what gets consumed by your livestock, then these ions can accumulate over time because you keep adding them with your top off water. You can mitigate the effect of ion accumulation with large water changes from time to time. If you're on city water, visit your municipal water supplier's website to see what's your coming out of your tap. 

 

Here's the page for the Fairfax County Water Authority, for example. And here's their 2015 annual report on water quality. Look on page 7 and you'll see things like 65 to 88 ppm average strontium, a little copper, and lead, trihalomethanes, haloaceticacid, coliform bacteria. Plus, when municipalities flush their lines, water quality can temporarily degrade.

 

So, when using RO/DI - at least you have some reasonably well understood baseline for the quality of the water that you're using in your tank. When you use tap water, your trusting that the water coming out of the tap is all that you would have it to be. When you have a tank with 10 years and thousands of dollars invested in it, you may wonder why you would quibble about a $200 RO/DI system with $40 of annual service expense.

 

Edit: Find FCWA's water hardness level here. 40 to 172 ppm.

[gmerek2]

We could probably get away with it but I don't think its worth the risk. I have seen my water come out orange after they flush nearby fire hydrants. Trace elements of copper probably won't hurt anything but like Tom said the ATO is constantly going to be pumping in so you probably wouldn't be able to slack on water changes. Plus they are finding trace medication in tap now you can't have a bunch of fish swimming around in Viagra water

[Jason Rhoads]

I should qualify that I do use RO/DI for my top-off water.  The tap is used only for water exchanges.  I feel that this helps mitigate the accumulating ions phenomenon that Tom mentions above.