Welcome... your tanks filter looks like a freshwater setup, you may want to get a hang on back protein skimmer. A protein skimmer filters the water better then a freshwater filter.
I use a hang on protein skimmer filter, a heater and a carbon filter. i dont use a sump.
I have been adding fresh water to top evaporation by my hands and dosing calcium and alkalinity and magnesium manually. Anyone can run a saltwater tank for not to much money.