Calcium test kits or not more reliable than alkalinity test kits. Calcium test kits always have a higher margin of error.Yes you are correct, looking more into it, apparently it’s because calcium test kits are more reliable? (Not in my experience they are far less accurate), they say you can use either but to adjust based on calcium.
To be fair, their instructions are a little mixed up, as they start by saying Increase the daily dosage – by continuous control of the alkalinity – weekly by 2.5 ml per 100 litres (26 US-gal) of aquarium system volume, until a constant carbonate hardness of 7 to 9 °dH is reached
But then later in the small print go on to say to follow calcium for dosing regulation.
I’m with you, I know where I want my alk, not to bothered if my calcium is a little off.
The reason why tropic marin recommends dosing according to CA is because the alk component of AFR is a slow release process involving bacteria. That is, you won’t see the alk increase immediately. It might take a day or two when dosing the first time, but after that it is usually observed with a couple of hours.