I'm not sure what is in Seachem Reef Builder. According to the label it's main purpose is to raise alk but maintain calcium and magnesium? I didn't know such an additive existed. Alk, Calcium and mag would precipitate out of solution in a small container. Kalkwasser is the only additive I know of that can maintain calcium and alk but magnesium will precipitate out of the solution.
I'd be willing to bet that Reef Builder is baking soda with additives like Borate to boost pH and whatever else they add to claim that it also maintains cal and mag. All that dosed into a tank can cause all kinds of imbalance and precipitation problems.
If you're looking to boost alk try regular baking soda or baked baking soda and dose manually or use with a dosing pump and test like crazy until you get it zeroed in. If you're looking to maintain cal and alk try 2 part or kalk. I don't think it's possible to dose all 3; cal, alk and mag with one supplement. You're likely getting precip from whatever is settling out of that product.
Make sure you are checking your alk often when using a product like that or you can get a spike and cause major problems.
