If it is above 13 dKH or so, I'd do some water changes with low alk water (maybe acidity it first to reduce the alk in it).
But in general, these events are self correcting because the precipitation drops that alk and pH.
I discuss them here in the context of limewater overdoses where pH is a bigger issue than alkalinity, usually. My tank has turned to milk without losing anything.
What is that Precipitate in My Reef Aquarium? by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2005-07/rhf/index.htm
from it:
The following important points should help in dealing with a limewater overdose:
1. Don't panic! These overdoses do not usually cause a tank to crash.
2. The primary concern is pH. If the pH is 8.6 or lower, you need not do anything. If the pH is above 8.6, then reducing the pH is the priority.
Direct addition of vinegar or soda water is a good way to accomplish this goal. Either one mL of distilled white vinegar, or six mL of soda water, per gallon of tank water will give an initial pH drop of about 0.3 pH units. Add either to a high flow area that is away from organisms (e.g., a sump).
3. Do not bother to measure calcium or alkalinity while the tank is cloudy. The solid calcium carbonate particles will dissolve in an alkalinity test, and all of the carbonate in them will be counted as if it were in solution and part of "alkalinity." The same may happen to some extent with calcium tests. Wait until the water clears, and at that point, alkalinity is more likely to be low than high. Calcium will likely be mostly unchanged.
4. The particles themselves will typically settle out and disappear from view over a period of 1-4 days. They do not appear to cause long term detrimental effects to tank organisms.
5. Water changes are not necessarily beneficial or needed in response to a limewater overdose.
