I am quite new to this hobby, have had this tank for around 3 weeks with plants inside. There are quite a bit of pond snails in there too, but that's about it other than some tiny seed shrimp.The tank was just fine the previous day but now, the s.repens developed holes in it and the zenkerI developed from purple into yellowish greenish leaves. there is also another plant which I can't identify which simply turned brown. The water is pH 6-7, 15 gallon tank with medium high lighting and filtration system. The tank temperature is around 25 degree Celsius. Can some one help me to identify the problem? Any help is appreciated!