Accidental Overfeeding and Nitrite Levels (Rosy Red Minnows)

I had to go on a business trip last week and my mother in law stayed
with my son (6). He has a 10 gallon tank with 3 rosy reds. I told
her to feed them a small pinch of goldfish food daily. When I
returned yesterday, the water was cloudy and my fish were huddled in a
corner. One was swimming cock-eyed. There was a boatload of food on
the bottom of the tank and 1/4 of a container of food missing. I was
LIVID. I immediately asked DH to help me with an emergency water
change/vaccuuming of the gravel. I had to change about 50% of the
water to remove all the loose food. After adding fresh, treated
water, the nitrite level was still through the roof (5 ppm). This was
a well established tank with no other issues. I then changed about
20% more water, and the nitrite level dropped slightly. Then, I let
it sit overnight and did another 20% change this AM. The fish were
looking a bit better, so I was happy. Nitrites were still high, so I
added Amquel + (just a teaspoon). That really knocked down the
nitrites and the fish improved greatly.

Anything else I should be doing? Besides shooting my mother in law?

TIA!

Beth