I wouldn't use feeder block. Not very nutritious and can pollute the water. Tank should have enough critters and algae to sustain the Fish. When you get back feed them an extra time each day for the first couple of days and they s/b fine. If you normally feed twice a day , increase to 3 times a day for 2 days. The third feeding should be a bit smaller then the other two. DO NOT OVERFEED. Hope this helps.