I'd get a pressurized co2 system for a 55g with a 4 bulb t5ho.
But you can use a liquid carbon, but at a tank that large, it will get costly. You can try generic Excel, which is Glutaraldehyde. Its much cheaper and can be diluted to excel strength.
Edit: oops, you said "NO" t5. You can go liquid carbon. Glut will save you money instead of buying a lot if Excel.