I have an empty 125 gallon tank that is completely cycled. I used pure ammonia (Dr. Tim's overpriced ammonia - no ACE store near me) to cycle it. If I bring the ammonia up to 2.0 ppm, in approximately 12 hours, it is back to 0.0. Nitrite has been 0.0 for 3 days now after a large spike. Nitrates are between 40 and 80 ppm (I cannot discern the different color reds used on the API chart.
I want to stock the tank on Saturday after a 90% water change. I only want peaceful fish, like Tetras, Platys, Danios, and Cory fish. The water comes out of my tap at 7.8 PH, 6 KH, and 9 GH. My TDS meter reads about 150.
I have an RO/DI filter unit and I have been toying at the idea of doing a 50/50 mix to lower the KH to the 3 range (and maybe pull the PH down a bit too.) Once the initial fill up is done, I think a 15% water change weekly is doable with an RO/DI mix.
I have a 29 gallon with 3 Mollys, 3 Columbian Tetras, and 2 Corys. I started out with 7 Tetras 10 days ago, but I think one of the 3 left is a murderer and has killed 4 of them. I want to remove them and the Corys and transfer them to the 125 gallon and turn the 29 gallon brackish for the Mollys (I will get more.) I do not want more Columbian Tetras as I have read that they can be aggressive and I am tiring of finding dead fish in my tank every other day.
So I have 5 fish to add to the 125 gallon tank on Saturday. My question is, how many more should I add at once to keep the bacteria colony that I have alive (or mostly alive.) I was hoping that maybe I could get away with 3 more Cory fish, 7 or so Platys, and maybe 6 or so Guppies. Will that be enough?
Sorry for the long post, just wanted to provide some background info. Thank you so much.