Hi Penny,
As Georgia said, the first thing anyone wants to know is -
Details of the substrate (what is it?)
Size of the tank
Tankmates?
Filter? type, size?
Diet? type, how often?
Water quality - how often do you do a change? how much? Do you use any chemical products in the tank?
Temp
Ammonia
Nitrates
nitrites
PH
And as a bonus if you can,GH and KH
If you cant do this because you have no test kit, then take a water sample (250 mlls) to your local fish store (just be aware, very few fish stores know much about axies, so take their advice with a grain of salt) come back here for better advice
Couple of things to start with -
* I agree , on the surface, the tank looks a little small - let's assume a new tank is not an option right now, so they'll survive there, its just not ideal long term - the problem with a small tank for you right now might be water quality. Two axies will dirty the water in a small tank faster than a bigger one, it's simply less water to dilute any nasties
* You mentioned you had left food in there for 3 days? Any un-eaten food should be removed from the tank 10-15 minutes after eating. just as any other waste, axie or plant or food, should be removed as soon as you see it.
Based on the fact you said you don't know much about water quality, and you tank is a little small, and it looks like you might leave food in there too long, i reckon any issues you have right now might be water quality related.
Have a look at the link Julia showed you , also have a search in the forums here for info about the Nitrogne cycle. Give your tank a good clean (vacuum the bottom) DONT strip and clean everything, just clean out left over food, plant or axie waste.
Do a 25% water change with de-chlorinated water today and perhaps in the next 2 days as well.
Get your water tested at the fish shop, and buy an API test kit for Ammonina, nitrates, nitrites and ph & a thermometre while you are there
I'm guessing the water has gone a little dodgy on you, doing that clean up and more than normal water change might help in the short term
Bren