Regarding the phosphate remover:
Most phosphate removers are granular ferric oxide and work in the same way. You need to have water flowing over it (so put it in a filter or a phosphate reactor) and the phosphate binds to it. It can only bind so much phosphate though before it stops working and then you need to replace it. How often you need to replace it depends on the phosphate levels in your tank.
There are other phosphate removing methods though. One is to use a refugium which contains macro algae such as Caulerpa and Cheato 9I would stay away from Caulerpa because it can "turn sexual" which in some cases has wiped out peoples tanks. The algae grows and absorbs phosphates and nitrates then you regularly prune the algae back which then removes the nutrients from the system.
On a similar vain some people use turf/algae scrubbers. These are basically areas which are set up to encourage rapid algae growth. Have a look at the thread below for more info:
http
/www.fishforums.net/index.php?/topic/253010-mega-powerful-nitrate-and-phosphate-remover-replaces-skimmer-refugium/
There is another option which is basically a liquid that you add to the tank which binds to the phosphate and then gets pulled out by the skimmer. I haven't used this yet though so cant really comment on it.
Regarding the mag cleaner:
One word of advice. when you are not using it make sure you put it so the inside part is out of the water. If you don't you will get marine critters growing in it, most of which will have hard shells which will scratch the glass when you use it.
Regarding mandarins:
Correct, the male has an elongated spine on its dorsal fin. Not sure on the court jester, personally I would recommend leaving both the court jester and the mandarins for as long as possible to make sure the tank is mature and you have a good pod and micro fauna population.