I am looking to buy a new reservoir, do you have any advice?
Choose the biggest reservoir you can fit into your garden and a lid to slow evaporation. Water is consumed and evaporates at a faster rate than the nutrients. So to prevent against exceptionally high nutrient concentrations, a big reservoir is recommended. The bigger the amount of nutrient solution, the more forgiving your hydroponic system and nutrient solution will be. As a rule, always make sure there is at least 25% more nutrient solution in the reservoir than the mount required to fill the entire system. Remember to check reservoir levels daily.