RO and pH issues.

"Todd Nicholson" wrote in message
ink.net...
You don't need to buffer the RO water you add for top-off water. RO water has
basically no buffering ability, so when it's added, it will instantly take on
PH of tank water. It will not bring your PH down. Something else is bringing
PH down in your tank (or simply keeping it low). You might check your salt
mix first and your SG, then check your Alkalinity. Adding buffer and calcium
to your freshwater top-off water is only asking for trouble.

-Todd

Why? It has always been a practice of aqaurists in the past to make sure when
adding fish or any other animals to your aqaurium that the pH and temperature of
the water they are in versus the water in the tank are the same. If you add low
pH water (with no buffers) to a tank containing water with a high pH, the
resulting pH of the tank will not be the same that it was when you started,
especially if there is no buffer in the make up water because it will deplete
the buffer in the tank water. Buffers in the tank water help, but they can only
do so much before they are depleted as well. This is especially so if you have
to add make up water fequently, as I do. Adding fresh water that has been
buffered to give it the same pH as the water in the tank will not change the pH
of the tank water. In fact, it will help prevent a pH change. Oh, and I've
used the same sea salt that I've always used (Instant Ocean), and didn't have
this problem until I started using RO water as make up water. As for calcium, I
would only add the calcium if the tank itself needs it.

"George" wrote in message
news:lyA8e.22828$Bb3.8461@attbi_s22...

"Ray Martini" wrote in message
...
That is totally normal for RO water. It has no buffering capacity at all and
is very acidic. When you mix in your salt mix, this will usually buffer up
the water and raise the pH.

I understand that. That's not the problem. The problem is using it
unbuffered as make up water to the tank due to evaporation. I now understand
that it has to be buffered first. In addition, I am looking at adding
calcium chloride to it to increase the calcium concentration in the tank
water (or at least preventing it from being diluted when I add the make up
water).

If you're using the RO water for a freshwater tank (which I do also), then
you have to buff it yourself with Arm and Hammer baking soda. A&H is much
cheaper than the pH up stuff and it does the same job. I'll sometimes use
the baking soda to buff up the water to the same pH as my tank when doing
freshwater top offs.


"George" wrote in message
news:2uo8e.21314$xL4.5103@attbi_s72...
I have a 35 gpd Ro unit (with carbon and sediment filters, no DI filter).
I've been reading up on RO this evening and found several references that
say that RO water can be more acidic than tap water (lower pH) because RO
membranes do not reject CO2. This concerned me since I've been having water
quality problems for some time and thought that it might be a problem with
my sea water not having enough calcium. I bought a Nutrafin pH test kit and
a Nutrafin Calcium test kit. I got some interesting results. For the tap
water, I got a pH of 7.5 with 60 mg/L of calcium. At present, the water in
my marine tank has a pH of 7.5 (yes, I know it is too low) with calcium at
280 mg/L. The RO water has a pH of 5.0! Calcium was essentially 0. I don't
know if it is normal for the pH to be so low in RO water, but I suspect that
adding this water unbuffered to my aquarium is the root cause of my problems
(thankfully, I have quite a lot of sea sand in the tank, so it does prevent
a pH crash below 7.5.). I understand that RO units do not always result in
a substantial drop in pH since it depends on the amount of dissolved CO2 gas
that is present in the feed water. Apparently, my tap water has a high CO2
content.

This is a good argument for strict testing of make up water, especially
since, in my case, I never tested the pH of the RO water, assuming that it
was neutral (which it is obviously not). I plan to start adding sodium
bicarbonate and calcium chloride to the RO make up water in the future, and
aerating the water for 24 hours prior to adding it to the tank. My
question is does anyone know of a computer program that I can use to make
calculations of how much of each to add? I can do it manually, adding a
little at a time, but it would be nice to be able to calculate it in
advance in order to approximate what is needed so that it doesn't take so
long to do or use up the expensive test kits. Another question. Since I am
going to add calcium chloride (turbo-calcium) and sodium bicarbonate,
should I also be worried about adding magnesium to the make up water?