Overwatering?

My 115gl has been planted for around 3 weeks now. I have misting on from 5 nozzles for 1min at 9AM and for 1min at 8PM using distilled water. I have 3x96w PC lights on from 8AM to 10PM (2 x 5000k, 1 x 6700k). The temp in the tank ranges from about 65F to 80F and the humidity is ALWAYS over 90%. The substrate is my own ABG mix: 2p orchid mix, 2p cocopeat, 2p sphagnum moss, 1p charcoal, and 1.5p peat moss.

Some of the bottom brom leaves have been curling a bit recently, and one brom (chiquita linda) even had browning leaves. I removed almost all the sphagnum moss the bases were wrapped in and we'll see if that helps.

Everthing else is growing pretty well, not sure how fast this stuff should be growing, but over the 3 weeks, there is definitely some new growth and leaves. Only some creeper cuttings are taking their time, we'll see.

Now to my problem. I have a Begonia luzonensis which is acting funny. Ever since maybe a week and a half ago, the stems have dropped towards the ground and have been laying somewhat flat.



I didn't think anything of it since i saw some new leaf growth from the middle and then even flowering, but today i noticed that the old leaves have started to brown around the edges.



I've read that it may be from underwatering, overwatering, low humidity, low light and too much fert, but most of these causes are ruled out. I'm thinking that it may be overwatering or that the soil mix holds the water too much. Any suggestions about this? I want to fix this problem ASAP.

Luke