Feed them morning and night. It should take them 3-5 minutes to each what you've given them. Watch them for 3-5 minutes after they get their food to make sure they're getting enough of it, and you should be good. A pinch is pretty average. Also, it's a good idea to turn off or unplug a filter and/or bubbles and/or anything else that would circulate the water so that the food doesn't get sucked up by the filter.