Hi there,
Try using air line tube tied to a long thin piece of plastic that is not easily bendible, you can then syphone the bottom of the tank very carefully and just check after that no fry have been sucked up.
Although pretty hardy fish, try not to move the fry out of the tank in order to clean as any drop in temperature due to movement can cause faulty problems.
Get your self an aqua one over flow filter and replace it with your sponge once they are a little bigger, you can use the sponges from the sponge filters to put on the end of the down pipes in order to not suck up and fry, start the filter on farely slow and as they get bigger, turn up the flow.
Hope this helps abit more.
Regards