Blue-greens wipe out - HELP Please !

Hi everyone,
I need some help. I am getting wiped out with blue-green algaes.
I have a 48" by 20" high by 18" deep tank with a Dennerle CO2 system. I
am changing so much water (am currently doing 50% twice a week) that I
am currently using Dennerle fertilizer like there's no tommorrow - which
is very expensive over here at 12 Fe tablets a week and 100 tabs for
26ukp... I'm starting college as a mature student at the end of
September and I need to find a cheaper (as less time consuming) way of
fertilizing my tank. Does anybody out there know how to make your own
fertilizer ? Can I use 'human' multi-vitamin tabs - or are the %'s all
wrong? Does anybody know what the essential vitamins & trace elements
are needed for good plant growth ? How much of each is needed ? Is
Sulphate of Iron (cheap here) the same as the chellated Iron needed for

Any suggestions (including other net-sources I could look to etc.) would
be a great help.

Thanks in advance,
Steve Andrews. 

"For those that think, life is Humer, for those that feel, life is
dispair & for those with blue-greens, life's a financial burden!"