These Frontosa will get up to 14 inches long. However they will grow slowly, so the 10 gallon will work for a little while. I have an 8" Burundi and a 3" Aqua blue. I get the aqua blue when it was about 1.5" back in February, and has only doubled in size in the last six months. Frontosas grow slow. My 8" Burundi, was about five inches when I got him in January, and he has grown 3 inches since then. You will need a bigger tank for sure. Eventualy, if you want them to be happy and healthy, you will need at least 80 gallons. Today you are ok for a bit.