I give my goldfish bug bites and they love them. The bug bites are pellets and I buy the goldfish specific ones that say medium to large fish.

Here's a link! Fluval A6584 Bug Bites Goldfish Pellets 3.53 oz, Medium to Large Fish https://www.amazon.com/dp/B0711CMGT5/ref=cm_sw_r_cp_apa_i_pJA.CbYTQGGDQ