At the moment I have 7 electric blue acra fry in a 24 lt tank with 1 seeded sponge filter would puttimg another sponge filter be over kill and cause too much water turbulence for the fry .So far they have been in there a week they have got bigger since last week bar 1 which still seem's the same size I managed to scoop them out sunday a week ago next day all the fry in the main tank were gone I do suspect the parents although I some of the other fish were picking off any that strayed away from the parents but for about 30 fry to vanish over night and always on the second day that I see the fry free swimming they suddenly vanish.