I did my usual 25% water change on my 20 gallon long last night after work. This morning my tank smells quite strongly. Kind of like it's regular earthy smell, only WAY stronger, maybe a little foul. I checked all my fish and snails, everyone is present and accounted for. Checked my water last night and this morning: 0 0 5ish. The only thing that's different is that I put a slice of zucchini in last night after the water change. Could that be causing the smell? I've only had the tank up and running for four months. Thanks for any thoughts or suggestions.