Have a large tank that has high calcium demands? You can run a calcium reactor, but you’re afraid of constantly low pH levels. You’ve considered a kalkwasser reactor, but you don’t think your top off system will be able to deliver enough calcium to meet your needs. So my question is, why not use both? Using both a calcium reactor and kalk stirrer can be pricey, but you negate the cons of each system by using them together. The kalk will raise your pH and keep inorganic phosphates low, while the calcium reactor will constantly feed calcium to your tank.