Other than the concern with the temporary change in chemistry, or a difference in cost, why wouldn't I discontinue the kalk?
I posted this last night but the server for rc went out , So here it is.
Many aquarists run nice systems without kalk via 2 part or a calcium reactor . Many use combinations of these techniques . It isn't necessary to use calacim hydroxide(kalk) ;but ,it's my favorite way to dose calcium and alkalinity.
I've been dosing kalk for about 6 years . My sps dominant aquariums have never done better than the last 3+ years with kalk as the primary alkalinity and calcium supplement . I have always done regulalr water changes which also add calcium and alkalinity as well as a small tweak with baked baking soda for a little extra alk (1 tablespoon every 5 days or so).
Earlier I used a caclium reactor with kalk dosing . That worked well for a while but ph continued to be an issue and I became mildy concerned about potential impurites from the CA CO3( aragonite media); it has been off line for more than 3 years now. As a new guy begging to learn and apply reef chemistry , I used two part( calcium chloride and calcium carbonate) but never got the balance right ,alternating between highs and lows and some precipitation. Kalk dosed as clear fully saturated ( 2 tsps per gallon of top off) from a still reservoir via peristaltic pump which provides small increments over 24/7 keeps up nicely with all of the calcium demand and about 95% of the alkalinity demand.
Other than the concern with the temporary change in chemistry, or a difference in cost, why wouldn't I discontinue the kalk?
All the changes in chemistry are not temporary. To iterate some already noted inthe posts above and mention a few more:To maintain calcium and alk levels an equivalent amount of additional two part will be needed to make up for that no longer provided by kalk.
Ph will drop even if extra baked baking soda is used. Calcium hydroxide ( kalk) disassociates in water .The free hydroxide snatches up CO2 to make carbonate. The CO2 in the water is thus reduced. More CO2 = lower ph ,as it shifts the carbonate ratio toward bicarbonate and carbonic acid ;away from carbonate; thus, lowering the ph and buffering capacity.
Long term use of calcium chloride( the calcium part of two part) will skew the chloride: sulfate raito in favor of chloride and off natural sea water ratios . Water changes and some magnesium sulfate for a portion mag dosing can offset this.
Kalk is self purifying. Impurities precipitate in the high ph of the kalkwasser( limewater) and settle in the slurry. Calcium chloride has impurites and , some marketed as trace elements in commercial two parts and some deliberately adding like a bit of magnesium. I've never found a pure calcium chloride, though many have levels of impurity deemed "acceptable".
