This may be a stupid question, but I wanted to be sure. Does cleaner water promise faster growing fish? Because my fry tank was long overdue for a cleaning and it seems like they aren't growing too quickly. Also, does a strong current affect growth at all? My filter is pretty strong and sometimes throws them around a bit.

i wouldn't say clean water guarantee's faster fish growth however along with a good balanced diet it will certainly help.

don't know if the current would make any difference tbh.

in theory a stronger current would lead to them expending more energy to remain in one place and therefore if they were fed the same amount the would grow more slowly as less energy would be put towards growth.

If by "cleaner" water you are talking about removing existing tank water and replacing it with new water, than yes, cleaner water has a large impact on fish growth...particularly regarding fry. Good feeding practices of appropriate foods and frequent water changes are of paramount importance in fry development.

-Brad