Thanks all for the info everyone right now it is running alright but I think I will put my skimmer intake out side and maybe add some Kalk at night when the corals start growing out some more.

Untamed, do you notice a drop in dkh from passing through the second stage?

Sorry, I've never attempted to measure that difference. In theory, the dkh should only be HIGHER after the 2nd stage.

The idea, of course, is that the CO2 reacts with the CaCO3. The more the CO2 successfully reacts, the higher the pH goes.

If you stopped the water flow through the reactor...added CO2 until you got to pH6.5...and then stopped CO2 and all flow...then the pH in the reactor would slowly rise back up as the reaction takes place. It wouldn't get all the way to pH 8.0 because the solution in the reactor would become saturated with CaCO3 and higher pH would start to recalcify the CaCO3. (which is what happens when you add too much Kalk too fast).

Since we maintain the first stage at pH of 6.5, any water leaving that stage will be at pH6.5 and therefore contains a LOT of residual CO2. That is unavoidable. That residual CO2 is the problem and drives down the pH of your tank. This is also why you can't flow water too fast through the reactor. Too high a flow rate just blows water and CO2 through the reactor and there isn't enough time for the reaction to take place. That's why slowing the flow rate of your reactor can actually make it deliver MORE Ca/Alk and why larger reactors can deliver more than smaller reactors.

With a multi-stage reactor, that residual CO2 reacts in the 2nd stage and causes the 2nd stage to be higher in pH. CO2 is delivered based on the pH in the first stage, so the 2nd stage is allowed to move higher in pH without causing additional CO2 to be added.

Sorry for the long-winded response!

Thanks for that, interesting reading. I seem to recall reading the second chamber can cause a slight precipitation of the alk as it passes over the 2nd stage media.

I have to add media to my 2nd stage every now and again. It dissolves away just as the 1st stage does...just a lot more slowly.

Hi there, I am thinking about adding kalk to my top up reservoir, would you mind telling me how you are doing it please.

Thanks

Steve

If your top off system is gravity fed to a float valve the kalk will constantly plug the float valve so that is not recommended. If your ATO is administered by a pump the kalk will constantly plug up the pump so that is also not a good idea. What you want to do is administer kalk in line with an ATO system incorporating a pump (like the Tunze or JBJ systems) through some sort of reactor or perhaps a simple container. A reactor like the one Precision Marine makes can be purchased or built DIY if you're a little handy. Or a simple container like what Tunze sells could be made out of an empty pop bottle. These inline systems also have the advantage of keeping your top up reservoir clean and limiting the exposure of the kalk solution to CO2.