New to group and a dilemma

Hi, I've come here with a bit of a dilemma. My grandson who lives with
me along with his mother, received a Spongebob aquarium as a gift. It's
1.8 gallons with gravel and an air pump.

Originally he was given two goldfish but a quick check showed that to
be a poor choice. They were taken back and I suggested a Beta but he
wanted two fish so he got 2 Zebra Danios instead.

The thing is, the more I look on line the more I find out that this too
may have been a poor choice. Not only that but I am clueless about
maintenance of the tank.

I asked at work, they have a beautiful 55 gallon salt water coral tank
with about 6 fish. I was told to only feed the fish on Mondays,
Wednesdays and Fridays because otherwise the tank will get dirty and
the fish will die. This has worked well for them because all of their
fish seem to live a very long time, and their Clown Fish is 10 years
old. I know this isn't a lie because I've worked there 8 years and he's
been alive since I started.

Now checking around I'm finding out I should feed them once or twice a
day. Also that the tank should have 20% of the water changed twice a
week. We haven't done it once in the two weeks he's had the fish. The
water is still clear, with no odor and the fish are pretty active. The
water was treated with "Stress Coat".

Also, when I have the grandson feed them, he's only given them one
broken up flake. The fish are so small that it looks like a lot of
food. They seem to eat most of it with very little falling to the
bottom of the tank.

So, could someone help me out and give me step by step instructions? Or
point me to a website for small tanks. It seems like everything for
small tanks is for a one gallon (or less) for Betas and without an air
pump.

Thanks,
Klane