Who Gives A Fish Forums

The issue with Vallisneria and Excel is well-documented - it's a toxic combination. In most cases, Excel will kill Vallisneria species, along with some other plant species. I won't get into the details now, but suffice it to say it's not a good additive for any planted tank.

Regarding lighting ...

I'm thinking Flourish Excel might be your problem with the jungle val - it's actually pretty toxic to Vallisneria. Also, 15 hours of light is way too much, consider getting a timer to cut it back to 8 hours a day.

I'm no expert, but compost in an aquarium doesn't sound right to me.

Aquasoil's known to leach ammonia. I'd stick with regular water changes, maybe twice a week, 50%. Your daily 50% changes seem to be working, so keep that up for now. Honestly, not sure I added much to the conversation here.