i dont find it any more work than having a brackish tank. every few days, or when the water looks low i check the salt. if theres too much salt in my eyes, i add fresh water to bring the sg down to the required level.
i try to do a WC every week. but sometimes the bills need to be paid first. so it depends.
the dosing of calcium in your dads mates tank will probably be for corals, or just to get more coraline algae (the red/purple stuff on live rock) to grow.
IMO, protien skimmers arent needed on small tanks. water changes are an easier and cheaper alternative. on larger tanks where the cost of water gets expensive, protien skimers begin to make sense i think someone said 100L of SW costs 20$? maybe. thats like £16. if thats accurate, i cant afford that.
and you can use basic filters in SW. i used a fluval 4+ in my salt tank for months with no negative effects. now i use a fluval 405. the trik is to use only the mechanical filtration. i only use the sponge. the 405 is basically for extra volume and water movement. the LR will cover most of your filtration needs in a SW aquarium.