Bill is right. Sugar is like adding gasoline to a slow-burning fire.I echo the "no" to the idea of using sugar as a carbon source. Don't even think of it.
In a NPT the carbon is supplied by the atmosphere plus the natural decomposition that takes place in the soil substrate. It is not necessary to add it in another form.
I added sugar to one tank about 20 years ago, and it killed a couple fish that night.
Just add more fish and/or snails and fishfood to the tank. Fishfood and soil organic matter releases carbon dioxide (and other plant nutrients) slowly and safely into the tank (my book, pp 78-82).