Can I get An African Dwarf Frog??

For starters, your tank is too small for 1 goldfish, let alone 2 and an algae eater. Goldfish are very messy, deep bodied fish. They will be bumping into each other if all housed in this tank together. An African Dwarf Frog, given the chance can and will jump out. I am searching for mine now. Poor thing, she is surely dead, jumped out 3 days ago. She was well over a year old, and just decided to escape. Please for the health of your fish, get a bigger tank before adding anything else. Try to stick roughly to this formula, 1 inch of fish/gallon of water. More is always better though. While your goldfish are okay when very young in a 10 gallon, they will outgrow that space very quickly. Really one goldfish in a 30 gallon is pushing it.