Starting a 20gal

[Kronk]

-I would get a single 150w MH there are some decent priced ones online sunpod?
-Fiji is going to be the best in terms of porosity
--2 koralia 1's would be 800gph of flow might want to look into the koralia nanos at -240gph
-hydrometer works fine for me
-i would go with better salt, kent or even tropic marin with a 20g it will last a long time
-reusing heater is a good idea
-the glass lid i would recommend against, it will rise your temperature evaporation is really the only way the water can cool down
-I do a weekly 3 gallon water change in my 20g
definatly get a skimmer, seriously
i know it complicates things but i would look at setting it up with a 10g sump you wont regret it just google it and you will see its not that much more work to setup and it will make things a lot easier in the long run

Best of Luck