yeah i think you have a couple months, once he reaches about 4-5in i would put him into the 55g with the rainbows, and by that time if you think they will stress each other then maybe you could have found a good deal on another 55g on craigslist or something. and you wont have to worry about stunting as long as you do enough water changes to keep the nitrates really low (below 20ppm) and yeah he is a great looking little ebjd just make sure to keep an eye out for parasites as this is the cause of most ebjd alleged "slow growth" as long as it doesnt have any parasites or bacterial infections you should be able to expect growth close to or the same as that of a regular JD