I think I found the problem to the pH drop. My tap water was fine, just got it tested. I recently turned off the lights in the aquarium to lower the temperature a couple degrees, but since my tank is planted my plants didn't get any light. This is what I read today:
"When CO2 is not present in sufficient quantity plants grow very slowly and will tend to stay smaller. Furthermore, biogenic decalcification can occur; this is, essentially, a last ditch effort by the plants to obtain CO2 by breaking down the salts in the aquarium water. As this process occurs, the pH level can raise a couple points in a fairly short period of time. This alone is stressful enough for the fish, but the problem worsens when the lights are turned off. When photosynthesis stops at night, the plants will stop breaking down these salts and the pH will drop rapidly."
If this is true, than that must be the case. All this happened the day after I turned off my aquarium light, and I now turned it back on. Any help is welcome!!