I can't stress enough make sure you use calcium carbonate and not cal/mag. The magnesium can be toxic and be a time bomb if your PH swings in the future with muck on the bottom of the pond.
You can't wreck anything with calcium carbonate. You can't have to much. It is a natural buffer and trys to bring you PH to 7.2 all the time.
If you can't get calcium carbonate and only dolomite lime then make sure you get samples and put in only the recommended amount.
Cheers Don.
Don, can you explain what it is about magnesium that is toxic? This is the first time I have heard of any danger at all from Ag Lime. Granted, too much of most anything can be considered toxic, yet Ag Lime (Dolomite,(CaMg)(CO3)2 ) has been considered the best, long term, buffering additive there is. Gross over application directly in the water is often recommended to increase the length of time between applications. Both Magnesium and Calcium are essential elements for good fish growth. It also dissolves slowly and can not raise pH over a maximum of 8.2, which is very safe. Some of the best fishing can be found in old Dolomite rock quarries.
