Re: puzzling, persistent substrate dampness
If you have no drainage outlet and you are using hard water for the fertilizer feedings you are likely going to be building-up salt in your substrate - particularly since you don't see any water draining into the bottom. This may not be your immediate problem if this is a young viv - but it will be an issue over time.
Your current problem could also be an issue with young substrate. Freshly mixed substrates that use un-composted organic components need a period of weeks to months to mature because the first stages of decomposition require nitrogen before they begin releasing nitrogen. This means fresh organics compete with plants for nutrients. Not sure if this is your issue but it could be - especially if you planted densely at the start.