Have to agree with supasi above. Sand is only very fine gravel after all and will not behave any differently to gravel from a chemical point of view. All my planted tanks are greywacke sand and it is not a problem. The plants look new as suggested and the whole system will need time to get established and create a balance. This cannot happen unless you leave them alone and "just look not touch." If you kept digging up your vegetable plants and washing them under the tap, leaving them with snails then goldfish I think the veg department at your supermarket would become your favourite place pretty quickly.