RO/DI question

[joander123]

hey guys, quick question about the filter.

I just set it up about an hour and a half ago, its made about 3 gallons of water so far.

I recall reading someplace that the first 5 or so gallons of water are no good to use because the filter is still breaking in, is this true?

thanks,
Jay

[fsn77]

It's a good idea to throw out the first 5 gallons, just to be safe. Many RO membranes come with a preservative solution in them, so you'd want to flush that completely out before saving any of the water for your tank.

[joander123]

ok, just checking. I was planning on doing that anyways, but its so depressing to watch 2 hours of water go down the drain lol.

[joander123]

another dumb question about RO,

if im just using it for top-off, do i have to add anything back to it before throwing it in the tank?

[Reefscape]

another dumb question about RO,

if im just using it for top-off, do i have to add anything back to it before throwing it in the tank?

nope, nothing at all...its fine as it is Jay....

Niko

[Pallen81]

another dumb question about RO,

if im just using it for top-off, do i have to add anything back to it before throwing it in the tank?

It's okay to put it back in for top offs as previously stated.

Just a note: Sometimes I add a tiny bit of marine pH buffer just to make sure the pH is correct since my RO unit lowers my pH to somewhere in the 6-7 pH range.

[joander123]

thats just what i dad pallen, i made a 10 gallon bucket, and added a tsp. of buffer to raise the ph of it to 8.3

I was just wondering, as i know that when you have FW tanks using RO, you have to add elements back. But i guess since its only top off, and the salt doesnt evaporate, most of the elements stay in the water with the salt, correct?

That is until you have corals and such soaking up calcium and what not.

[Reefscape]

But i guess since its only top off, and the salt doesnt evaporate, most of the elements stay in the water with the salt, correct?

That is until you have corals and such soaking up calcium and what not.

Thats a correct assumption there Jay....

Niko

[Squawkbert]

Don't trust pH readings of RO/DI water right out of the unit.
By definition, there are few or no ions in the water, therefore it has no pH.

If you insist on doing it anyway and have a pH meter, adding a trace of KCl will allow the pH meter to work without biasing the result. Keep in mind, however, that this result will be highly unstable as the first bit of anything remotely acidic or basic to fall into your water will dictate the pH until something else changes it and/or buffers it.

Think of measuring pH of RO water as being analagous to measuring sound pressure in a vacuum...

[joander123]

yes, it makes sense. So are you saying that it doesnt serve much of a purpose to buffer RO water?

[clown-lover]

I have never had an issue with RO water changing the PH of my tank. But then its probably going to depend on your setup and if you have things like aragonite as a substrate to help buffer your water.

The only thing I add to my top off water is Kalkwasser so that my used calcium is also replaced at the same time. And I don't do this all the time either.. It depends on my current calcium test.

[fsn77]

I use our auto top-off to dose alkalinity buffer to our reef, which allows me to very easily keep alkalinity levels higher and more stable than I could testing / dosing every couple of days.

I think the point is there is little value in trying to target and measure a specific pH value in your RO/DI water via adding pH buffer. Because RO/DI water is so pure (and poorly buffered -- non-resistant to a swing in pH), it only takes a small addition of anything acidic or basic to cause a drastic change in the pH of the RO/DI water.

There's plenty of reasons to add buffer or calcium to RO/DI top-off water. Calcium and alkalinity are consumed by coralline algae, snails, and corals... dosing those back into the system via top-off water can greatly simplify your dosing schedule. However, it's best to only maintain either of those levels via top-off after getting a handle on how much your particular tank is consuming and how much water is evaporating each day.

[Squawkbert]

Right - don't sweat your RO's pH. If you want to use it to supplement Ca or whatever, fine.

[joander123]

alright, good stuff.