I would be willing to bet that a lfs, dealing in quantity of scale could qt fish for around $0.50 a day, or $28 added cost on average. Smaller fish for less larger fish for more, but that would be a rough average. But more important to the average home aquarist not the die hard reef junkies is the time. If doing prophalytic treatments your cu gets too low, start over. If it goes too high you killed the fish and start over. Ever notice how live Aquaria guarntee does not even cover the full qt time for a fish? With a store front, there are employees who are there to monitor the tank all day. People who do it often enough that they become proficent. I speak from expierence in saying that qt can be daunting. Watch for ammonia, test water daily, if ammonia climbs (tang in a 20 long can spike ammonia in no time) water change. Dose the water before adding to maintain levels. Matching all the parameters for an average end user is a bit intimidating. Many die hard reef junkies forget not everyone can dedicate the same time and money to their tanks. I am home for 2 days or so every 2 weeks. I leave my wife in charge when I am gone, and she is scared of the process. If you kill a chromis, you are out like $8. Kill a purple tang, you are out $200.