In growing greenhouse tomato (Lycopersicon esculentum Mill.) using the nutrient film technique (NFT), HNO3 or H3PO4 is usually added to offset the increase in pH of the recirculating solution. For economic and environmental reasons, HCl would be a possible substitute for either HNO3 or H3PO4. Therefore, experiments were initiated to evaluate HCl as an alternative acid in controlling the pH of the recirculating solution in NFT-grown greenhouse tomato. The effects of HNO3, H3PO4, and HCl on the growth, fruit yield, and fruit quality were quantified. In 1995, these effects were tested using `Trust' and `BST 7804' at a recirculating solution pH of 5.5, 6.0, or 6.5; in 1996, only `Trust' was grown at a recirculating solution pH of 6.2. In the 1995 experiment, genotypic differences in marketable fruit yield tended to be smaller when HCl was used to control the recirculating solution pH at 6.0 than when either H3PO4 or HNO3 was used. In `Trust', at a pH of 5.5 under the HCl treatment, fruit quality tended to be higher than in other treatment combinations. In 1996, over a 45-day period, the concentration of Cl− that accumulated in the recirculating solution from added HCl was 313 mg·L−1 (313 ppm). There were no significant effects of the treatments on the growth, fruit quality, or yield of the crop. The total marketable yield was better when HCl had been used, likely due to high fruit production at the early part of the harvesting period. Potential savings for the season can be achieved if HCl is substituted for H3PO4 to regulate the nutrient solution pH in NFT-based greenhouse tomato production.