Feed for the species
Choose food appropriate to the fish’s diet and mouth size. Distribute it so shy or bottom-dwelling fish get a share. Start with small portions and watch for leftovers; juveniles may need a different schedule from adults. A varied, appropriate diet is more useful than feeding a large amount.
Test and record
Record ammonia, nitrite, nitrate, and pH with the date and tank name. Note whether readings were taken before or after a water change. Compare trends with feeding, additions, and maintenance. A clear-looking aquarium can still have a water-quality problem.
Change water deliberately
Use actual water volume for your calculations. Treat replacement tap water for chlorine and chloramine, and match its temperature. The water-change tool estimates nitrate dilution; use repeated tests and species requirements to choose the amount and frequency. Evaporation top-offs do not remove accumulated dissolved waste.