what kind of sand are you using? and what is the ratio of laterite in your substrate? sand is generally not the greatest as it compacts and doesn't allow for proper growth of roots.
also, you don't say what other fertilizers you're providing, so i'm going to assume that you're not. you should read up some of the posts in the Fertilizer forum. right now you're not providing sufficient nutrients for your plants, as you're only providing micro nutrients, and need to provide macro nutrients.
you should also look into going either DIY co2 or pressurized if you can afford it. but this depends on how big your tank is, because even though excel is a great source of carbon, it's also a pretty expensive alternative.
hopefully this gives you some answers to why things are happening in your tank.
also, you don't say what other fertilizers you're providing, so i'm going to assume that you're not. you should read up some of the posts in the Fertilizer forum. right now you're not providing sufficient nutrients for your plants, as you're only providing micro nutrients, and need to provide macro nutrients.
you should also look into going either DIY co2 or pressurized if you can afford it. but this depends on how big your tank is, because even though excel is a great source of carbon, it's also a pretty expensive alternative.
hopefully this gives you some answers to why things are happening in your tank.