As I understand it, dolomite is a form of limestone - calcium, magnesium, and a carbonate. That carbonate is, ideally what you want for your kH..... If it is not raising your kH sufficiantly, then I have to assume that it is not doing the job for some reason.
You can add baking soda - it is a very common carbonate - and this will raise your kH. It will also raise the pH, though..... If your pH is always the same reading, every day, and your kH is at least 50ppm (I like 100ppm myself) then I would not fool too much with what you are doing.
Anytime you start a treatment in a tank, it is wise to continue the treatment to the end, unless the fish dies or has obvious bad reactions to the treatment. Parasites and bacteria, etc. will always have, within a population, organisms that are more resistant to treatment than other organisms. Your first rounds of treatment can eliminate the majority of weakest members of the population, and your fish may appear to get better. But if the treatment is not completed you will be potentially leaving alive members of the bacteria or parasites or whatever that were more resistant to the treatment. You stop treatment, and within a matter of days/weeks, the problem is back. Except that this time, the nasties are resistant to the treatment you used and it will not work. It is always better to complete a full regiment even if the fish appears to get better.
IF you have stopped treatment, though, it is probably not worth it to go back and retreat if you are not seeing any symptoms on the fish.
When ever you add a new member to an established tank, it is ALWAYs wise to quarantine the new fish. It may have problems that are dormant in the tank it came from, but, stressed and introduced to a new tank, the problems may pop out. You want to see those and treat them before they infect your established tank. KEep in mind, though, that you may ALSO have problems in your established tank that your current fish is immune to, but your new fish, stressed and all, will fall prey to! It is a worrisome thing - adding new fish. It requires that you keep a VERY close eye on the fish every day for a few weeks following introduction - AFTER a quarantine period!
I would suggest starting up the filter you will be using on the quarantine tank on the established tank NOW and getting it cycled nicely - in preparation for quarantine. Mix media, set them both going on the established tank. Another plus with that method is that you will be introducing the new fish to anything that may be in the established tank while it is in quarantine - and easier to treat!
I have not noticed that the blues or blacks are any less hardy than the reds/whites, except that they seem to be a bit more "rare". Any time there is a smaller population of a certain type of individual, they may tend to be selected more for color than hardiness - and may be a bit more inbred. It is so individualized that.... you just cannot tell. Find a fish that you really enjoy - one that makes you smile everytime you look at it. Study it carefully - and only take it if it appears healthy. Then quarantine it well, keep your eyes open, keep your water clean, and ENJOY!!!!
Orandas, Lionheads, Ranchu - they are all lovely fish.