To be frank, you have no business keeping any corals without an alkalinity test kit, and stony corals without a calcium test kit. You should also be checking your nitrates and phosphates. You can’t say you have good water quality if you’re not testing those parameters (getting your water tested every now and then at an LFS is not adequate, parameters can significantly change in a short amount of time, especially in a smaller tank). These are living animals we’re talking about, you have to buy the tools needed to properly care for them before buying the animals. So get some test kits (and any other equipment you may be missing) before you buy any more animals to put in the tank.
In the meantime, we’ll need some more info before we can try to help you. What kind of water/salt are you using, what are the parameters that you can test for (temp, salinity, etc), how old is the tank, how big is it, and how long have you had the corals?