@Randy Holmes-Farley I just noticed I am having a similiar issue. To be clear, the kalk container has precipitation that is expected. I have my pump situated to not pull mud from the bottom. However, I recently noticed that when the kalk water is added to the saltwater aquarium, fine precipitant forms and floats around for a while. Is this problematic? My current plan is to change where the kalk is dosed to be higher flow and mix up better. Any thoughts on this?
No, that floating stuff is not a concern. It is likely some magnesium hydroxide that will redissolve.
What is that Precipitate in My Reef Aquarium? by Randy Holmes-Farley - Reefkeeping.com
Precipitates Where Limewater is Added
When limewater is added to seawater, a cloudiness can form almost immediately (similar to that in Figure 3, although not usually that intense). This initial cloudiness is magnesium hydroxide, Mg(OH)2, and it forms when the water's pH rises into the low to middle 10's. Theoretical and experimental reasons for believing this material to be Mg(OH)2 (and not magnesium carbonate or calcium carbonate, for example) are given later in this article. As the limewater is mixed in, the local pH around the particulates drops, and as soon as it drops below pH 10, the magnesium hydroxide dissolves.
If the limewater is not allowed to disperse rapidly enough, meaning that the pH does not drop fairly quickly, additional precipitates can form, especially calcium carbonate. Additionally, if the limewater drips onto surfaces in contact with seawater (such as the sides of a sump, Figure 4), bulk calcium carbonate can form on those surfaces. This precipitation takes place primarily because the limewater has pushed the CaCO3 supersaturation very high by converting much or all of the bicarbonate into carbonate. Since the precipitation of calcium carbonate can be slow to occur, rapid dispersal of the limewater doesn't lead to much or any precipitation of calcium carbonate. But if a region maintains high pH for long enough, calcium carbonate will precipitate. How long this process takes depends on the degree of supersaturation, but can be on the order of minutes to hours.
Figure 3. The transient cloud of magnesium hydroxide that forms when high pH additives are added. In this case, the alkalinity portion of B-ionic was added to a fairly still portion of one of my reef aquaria.
