How is water managed and reused in a RAS system?

RAS recirculates and cleans the same water so you use only a small amount of fresh water as top up. Water from the fish tank passes through a mechanical filter or drum filter that removes solids, then a biofilter where beneficial bacteria convert toxic ammonia to nitrite and then to safer nitrate, then often a degasser to remove carbon dioxide, oxygen addition, and sometimes a UV unit to reduce pathogens, before returning to the tank. You must monitor dissolved oxygen, ammonia, nitrite, pH and temperature regularly, because the biofilter is alive and can be upset by overfeeding or a sudden chemical change. Continuous pumping and aeration are essential and need power backup. This is skilled work, so learn it hands on and keep your Fisheries officer's contact for guidance.