Most of those parking and industrial light fixtures are sodium lights and not suitable for a tank. If you can find MH fixtures you can use them but you will have to change the bulb to something with the correct spectrum. The ballasts are not interchangeable. They are about a hundred bucks each. As was said, they get very hot and are very heavy. I used them because I had them but I am very glad I now use LEDs.
As for the mortar, it just has to be regular brick mortar, not fast drying or anything else with epoxy or anything else. It is very cheap, practically free. A five lb bag is probably 3 bucks.
My wife's Mom died this morning at 12:30. She was 90 and suffering very badly for the last couple of weeks so it was a relief when she finally passed but it was very draining, especially for my wife.
Thank you for asking.
I had these lights left over from lighting up the Plaza Hotel in Manhattan and used them for a few years on my tank.
Here I am installing one on the Plaza. And doing some CAD welding on a New York City garbage incinerator.