I wouldn't worry about chemicals for NH3 spikes. The exception to that would be some booster for the sand bed/filters with bacteria and/or coenzymes in it. Rocks and sand after 6 months and fish in there will handle it just fine. No doubt the bristle worms, shrimp and crabs have put an end to that food source by now if it died, so that shouldn't cause you troubles worth adding nasty chemicals for. However some carbon wouldn't hurt anything and some may say phosguard wouldn't hurt anything.