Managuense always have large quantity of fry. One thing that I have learned through experience is that the fry are very sensitive to solid waste in the tank. For the longest time I would suspend siphoning the gravel while the fry were free swimming. I had huge die offs. I asked Jeff Rapps what the problem could be and he nailed it. Now I move the free swimming fry to a seperate tank with no gravel and do a daily or every other day water chnge to get the crap off the bottom.
One other thing. You need some kind of a gauze pad (filter bag...nylon stocking...something) around that filter intake. They will get sucked up inside pretty quick.