100 rupees
Some were.
Every month.
somme
Metal and iron depends on tank
Recycling centers pay for scrap metal by the pound. Therefore, how much you can get depends on the size of the tanks. There is not a very big market for used hot water tanks,for safety reasons. You may be better off trying to sell the tanks as scrap metal.
one time a month
SCUBA tanks are metal (usually steel or aluminum) that are filled with compressed air. This is loosely related to a pneumatic system.
Tanks that were still in good condition were used in the Korean War. Many tanks and planes were scrapped and the metal melted down to make new jet planes.
I think metal tanks are needed. Many newer have plastic.
Aluminum core, plastic side tanks.
I would say no because most halogens have low kelvin ratings and the light they put off is too yellow/red to sustain coral growth. Go with a 14,000K HQI metal halide with supplemental VHO actinics if you want the best color and a lighting fixture capable of keeping the most light demanding organisms (SPS, clams, anemones, etc...)
Bladder water tanks are relatively durable, however they will not last as long as steel and other metal water tanks. They are very favorable, however, for when you need your water tank to be mobile, as they are easy to transport.