Originally Posted by Don135
I mix my RO in a 33gal rubbermaid for weekly water changes. First, you could only make the amount of water needed for one water change. I have all my reconstitution chem's premeasured and determined for the 33 gal. can and drain my tank down to a predetemined mark on the tank and use the entire reservoir.
The other option for making more RO water than for a single water change would be to put gal. (1, 2, 5, etc.) increments with a permament marker on your mixing container, or a premarked dipping stick. After your water change determine how much RO your putting back in to fill it back up. If you re-calculate your soda, mg, etc. to reach your targets on a per gallon basis (or any preferred unit) you can multiply it up to the amount of new RO water you use to fill it back up. You just have to keep track of it, especially if it varies weekly.
I use a gram scale to measure everything out and can get pretty accurate (.01 gr.) with my measures. I don't think a TDS would give you all the necessary info to keep track of all the individual ratio's (mg, Ca, soda, KH, GH, etc.) as all molecules are factored into TDS condictivity not just the one's which make up GH and KH respectively.
Hope this helps...Don
Thanks Don those are some good ideas.
I guess my idea with TDS is that starting from RO water with TDS 0, I add GH until I get my desired level, then measure TDS and write that down.
Next, I would add KH until reaching desired level, then measure TDS and write that down.
Now I know the TDS values for this volume of water at point 1 and point 2. My theory is that once I do a water change and have say, 2/3 the volume in the tank, I can fill it back up with RO, the TDS will then drop, then I can add GH and KH again until I hit both of the values recorded previously.
Maybe that wouldn't work though.. I have thought more on this and I think it's probably easier to just dose GH and KH straight into the tank during water change. It's a smaller volume of water that is the same every time.