What are the readings of ammonia? There must be some reason why this has happened. Have you turned your filters for too long? Have you cleaned your media out under tap water? has something died in the tank and you haven't noticed? Okay, I would feed extremely sparingly at the moment, you want to reduce the amount of waste. Also, I shouldn't start packing loads of chemicals into the water. Remember that using chemicals can sometimes reduce the amount of oxygen in the water, for this reason, don't turn the temperature up too high because this can have the same effect.
Cloudy eyes can certainly be a sign of poor water quality and irritation. Are the fish breathing heavily at all? are they hanging around the surface of the water or at the inlet from the filtration. If they are doing none of this, then I don't think the ammonia level is dangerously high. In my experience, when there are high toxins in the water, fish behave very differently because they obviously can't breathe and probably feel poorly.
Please post your water readings. It's definitely a good idea to try and find out why this has happened, if you can come even stop it happening in the future. You said that you overstocked, exactly how much are you overstocked? Pool water conditions are often caused by overstocking tanks
I would certainly carry out regular water changes at the moment, 25% every day if you've got a heavy stock of fish. I think you would be wise to carry on using the ammo Lock, this will certainly help reduce any distress caused to the fish.
