Something similar happened to me. I had three tanks running at once and there were all just getting started with or finishing Level 2 environment, and only had Majic Fish #1

Just mixing up the breeding happened to result in Magic #6, but he didn't survive long.

Then I happened along to get Magic Fish #5, and two of those in the same tank kept each other alive and I was able to get #7 and keep those alive long enough to sell to earn the bucks to get started on Level 3 envirnoment...

(I still don't have #2, #3, or #4 in that tank, but have found them in others...)