I have 12 forktail blue eyed rainbow fish (4 males and 8 females) in a 15 gallon tank. I have an aquaclear 30 with a sponge, purigen and matrix. I also have a double sided sponge filter and plants. After a week with no water changes I still have no ammonia, no nitrites, pH is 7.2 and nitrates are 20. There is no fighting, they’re spawning and very active so do I need to move them to a bigger tank? I have a 45 I’m in the process of stocking but I don’t want to move these guys and stress them if they’re fine then I can figure out what to do with the 45 - little overwhelmed with the choices.