Now i got PL lights and i know that i would have to change the tubes every 6mths or a year. then today i noticed that one PL tube would cost me $85. I have 2 PL fixtures which would cost me $170 to replace the tubes. If so, i might as well upgrade to MH for $200 and replace the bulb every year for abt $100+. My tank is only 12 inches high and its not convincing to change to MH. can anyone give some advice?