The ole evil buffer product question

Karlsbad

Karlsbad

Sharkbait
Sep 23, 2003
231
0
0
Chicagoland
Visit site
OK so a lot of people use RO water. I want to start using 50% RO water. The phosphates in my tap water are 1.5 ppm up from 1 ppm two weeks ago and I suspect they may have been fluctuating even higher for some time.

Everytime buffer products are mentioned its a freaking lynch mob here. But there has to be a large number of closet buffer users given the number of RO users. I want something simple(ie not adding crushed coral or the moss from the lowermost 3 feet of a tree that's only found in the upper 1/7 of a remote island)and reliable and stable that won't hurt my little buddies and won't add evil phosphates. I don't want to debate or explain my reasons for using RO water if you don't mind, but can I get stable results using some good brand bicarb product carefully, say like RO right and a Kent or Seachem buffer and letting it sit and aerate between the addition of RO right and the pH product? I'm wanting to add 15 gallons tap water and 15 gallons RO water weekly. My tap (and current tank)water has a ph of 7.8, 120 ppm GH, and alkalinity of 150 ppm.

I think I'll be buying a fancy pen too :)
 
If you use 100% RO then RO right will be okay. But that can be expensive. Here is what I do. I add about 90 % RO and 10% tap, treated of course. My water is so hard, anything more than that, I get a huge ph swing. I have kept my parameters at the following:

ph- 7.2
gh-75
kh-120

I add RO right every other water change, which for me is about every day. I'm starting to think the RO right is not doing me any good, but I'm afraid to change my routine.
 
There is no way to get a valid pH right out of a high-rejection rate RO unit producing very low TDS (high purity) water. Ditto for DI water. Without RO right or comparable mineral mix (~Equilibrium, etc.), you cannot do a valid pH.

If you are set by pressure and rejection for only moderate TDS output, you can read pH.

There have to be some minerals present to read pH.

Folks - including me - poo-poo the routine use of buffers in tap water because 1) many are phosphate based, causing more problems than they cure and 2) because they tend to be very short-lived, increasing the TDS of the water until diluted out by partials for short effective lives. Too many folks have the mistaken idea that all fish must be kept at some magic pH close to the pH of their native water. This is false. Most fish are quite adaptable to water parameters. Some, particularly blackwater fish, do need low-GH water for breeding as the egg membranes are far more sensitive to mineral content than the adults. Over-riding the pH of tapwater by adding more material to the water is not, repeat not, reducing the mineral content of the water and is therefore counter-productive.

Reconstituting some mineralization in RO/DI water is not the same thing as adding buffer to tap water, it is needed in a captive closed ststem as straight high-purity RO/DI is not suitable for long-term support of fish.

Apples and oranges, don't get the two situations confused.
 
Originally posted by RTR
There is no way to get a valid pH right out of a high-rejection rate RO unit producing very low TDS (high purity) water. Ditto for DI water. Without RO right or comparable mineral mix (~Equilibrium, etc.), you cannot do a valid pH.

If you are set by pressure and rejection for only moderate TDS output, you can read pH.

There have to be some minerals present to read pH.
Click to expand...

Why is that? Granted I'm not up to speed on my pH indicator theory, but if you were able to remove all non-water molecules, should the water's natural equilibrium set up a pH 7.0? The indicators measure H+, not minerals. Or are you just refering to CO2 equilibrium and the need for it to re-equilibrate post RO?
 
Originally posted by happychem


Why is that? Granted I'm not up to speed on my pH indicator theory, but if you were able to remove all non-water molecules, should the water's natural equilibrium set up a pH 7.0? The indicators measure H+, not minerals. Or are you just refering to CO2 equilibrium and the need for it to re-equilibrate post RO?
Click to expand...

I could be wrong here, tell me if I am, but I think DI water comes out neutral and ends up around 5.5 - 6 after C02 dissolves from it or permeates into it or does some other thing that CO2 does. Don't ask me why. I actually thought that was the case with RO water as well, which is why travelinman has me confused being that he just adds RO right, which I understood to not directly affect PH other than providing hardness, yet he has a pH of 7.2.
 
Karlsbad, how hard is your tap water? You may not need to add any buffers at all. If you were planning to use 100% RO/DI water, you'd definitely need to use a buffering agent (and add trace minerals back to it as well) because being pure water it would have essentially no buffering capacity - but you're planning to use 50% tap water/50% RO water. If your tap water is even moderately hard, when you mix it with the RO water it will add all the buffering capacity you need.
 
Yeah, I understand that. If you use DI, then you remove carbonate & bicarbonate. CO2 equilibrium shifts, lowering pH.

What I'm wondering is why RTR said that you can't measure pH without minerals. I can understand that the pH you measure will be different than post-CO2 equilibrium/addition of RO right or minerals. But can't confuses me.
 
The problem lies in the fact that there are no buffering agents in pure RO water. A tiny bit of CO2 dissolves in the water forming carbonic acid then the pH plummets, the water comes in contact with something alkaline then the pH soars. Each pH measurement you get can be valid, but it can also change radically in a few minutes.

HTH,

Dave
 
Happychem - if you have high-quality water in the lab, try it - you need eletrolytes for the pH probe to work. We always used resistance - it will still work up to WFI (which we generated and used for our cultures). Probes are too erratic in low TDS water, cannot be validated. Direct electrical resistivity can be calibrated.
 
You must log in or register to reply here.
AquariaCentral.com
Top Bottom