If I went that route and went and got the fish tomorrow and did daily 50% water changes how long would you think it wouldThat’s similar to a mini cycle, the original amount of bb in your filter was enough for the amount of waste your original fish were producing. Now with larger fish creating more waste your bb colonies are not big enough to hand the additional waste being created, hence why you have seen a spike in ammonia. It could take a weeknor two for you bb to catch up to the new bio load. I would hold off as long as you can to get new fish.
Or if you don’t want to wait go get the fish and do daily 50% water changes until you get constant 0 ammonia and 0 nitrite readings.
take roughly to get the levels to
0, because I am leaving for vacation in about a week and a half and the person taking care of my fish while i’m gone will not be able to do the WC’s.