Something that is’t common knowledge is that most people overfeed their fish. They do everything right, until they follow directions on food packaging. Back when I was younger, we owned Betta fish. The packaging recommended 8 pellets, twice a day. The fish died rather quickly. We asked a vet and they told us we basically killed our fish by overfeeding it. I’m not sure about other species, but Betta fish will eat everything you feed them, even if it’s way too much. Some packaging recommends as much food as they can eat in three minutes. This is way too much. Fish food companies need you to go through the food and buy more, so take their advice with a grain of salt.
A test for your fish is to check their stomachs. There should only be a slight bulge after you feed them. A Betta’s stomach is only about as big as it’s eyeball. You should only feed them enough food that would equal their eye size. This will create the perfect sized bulge. Here’s a website with bulge sizes. It’s a little unclear, so I’ll post a picture at the bottom of my female Betta overfed and then normally fed.
My tank came with a sample of food. Probably a good 40 pellets. This could easily last me 20-30 days, depending. The Aqueon pellets are very small, so most days I feed Thalia two. Her stomach swells slightly and disappears before her next feeding.
I highly recommend clicking the pictures to enlarge them. Top is overfed, bottom is normal feeding (bad lighting sorry).