first off the disclaimer: I have a fledgling understanding, so if some of the real experts jump in with better info by all means disregard mine.
I like the sound of Mg or Ca bicarbonates instead of the sodium bicarbonate. If I wanted to dose a combination of MgCO3 and CaCO3, what is a good ratio? I realize my tank might have specific needs that would dictate something different; I am just looking for a good starting point.
I prefer the MG and Ca additions as well, but IME they are slow. As far as a ratio, I personally have gone for the idea of adjusting KH via these compounds with little or no regard to the CA and MG I get from them. It seems to me to be trivial amounts at best. even with pretty heavy consumption of KH, my crished coral was maintaining Ca levels well below 20 ppm.
As far as a dosing suggestion, I use the Dolomitic lime sold by Gregg watson, as well as crushed coral. The finely ground dolemite will cloud you tank when it is added, but it seems to clear up within a few hours which indicates to me that it is dissolving fairly rapidly for a dolemite product. The crushed coral takes a few weeks to really balance out and start working well, but it does do a nice job of counteracting consumption once a system is estabilished.
And what about KCO3..? Is that used/needed in a tank?
I am not familiar, but if you have plants, K is a macro that must be provided by some means. If you are dosing K via another vector, then you could easily use KCO3 and adjust your other K dosing accordingly. If you can find ratios of K-CO3 then Someone here can help figure out how much to use.
Also, I had a big sea shell that my mother decided looked nice and plunked in the tank one day (and it did). I kept in there just for her, but recently I failed to put it back after a small disaster that forced me to tear down the tank, and I am wondering if it was adding to the CaCO3
Almost definately it made some contribution. How much could only be determined by putting it back and monitoring. I have some crushed coral actually mixed into the substrate of one of my small RFUG tanks, and that is the only tank I don't have to add dolemite to weekly, but once again it doesn't seem to help much with Calcium only with KH.
Also, what happens to the Ca and Mg ions as the CO3 is consumed? Do they form other compounds and/or precipitate? (sorry if that seems like a goofy question - I'm not sure on that bit of chemistry)
Essentially whatever calcium and magnesium you add will contribute to your total GH minus whatever is consumed by your plants. The big question in the back of my mind is what your GH numbers are to begin with. My experience in plants is with Brutaly soft water, that I recently learned has virtually no Ca. If you have a decent hardness level and aren't dosing Ca or Mg, then you may not need them necessarily, but IMO it would still be more benificial than the addition of sodium via Baking Soda. Please understand that I have used baking soda extensively and the sodium levels never reached a point that could cause any problem I know of, it's just that when using baking soda, I add something I don't need that contributes in some extent to TDS levels Whereas the Ca and Mg are more naturally found in freshwater, and used by plants/snails/shrimp.
Also, doesn't the CO2 <> Bicarbonate equilibrium also involve carbonate? If so, does it matter if Carbonate or Bicarbonate is used, since the other is created to allow the CO2 to balance out?
As far as I know for our purposes with fish tanks there is no difference between carbonate and bicarbonate. both do the same thing for us in the same way. the chemical processes at work are something I haven't investigated, and honestly I have never compared ratios to see if Calcium carbonate did more or less than sodium bicarbonate by volume. I would imagine a difference, but have never had the urge to study it.
dave
