Fish feeder blocks dissolve over a period of time and release food for your fish. While dissolving feeding blocks may sound like a good idea, they are not an ideal choice for bettas. Most food blocks are for omnivorous fish and do not contain the nutrients your betta needs. You must use specific betta block feeders for the proper nutrients. These food blocks also dissolve at an uneven rate. This can leave your betta with too much or too little food. As the food block dissolves, it can cause issues with your water quality, as well. Without enough water movement from your filter, the block may not dissolve all the way.