1600w of flourescent lighting isn't the same as 1600 w of HID lighting, which is what that formula that you are probably thinking of is based on, the one that tells you you should get 700g per month.
400g under flouros isn't actually anything to scoff at. Could you do better, yes.
When you said you had to stake up your plants that was a HUGE hint right there. Flourescent lighting does not penetrate the canopy the way that HID does and if you must flower under flouros, your goal is to expose as much of the plant as possible to within a few inches of the light. This means in practice that you want a VERY flat canopy. A sea of green with clones flowered IMMEDIATELY after rooting and planted out in quart pots, or a SCROG into a net are ways to accomplish this. You want a continuous canopy nearly touching the lights.
No part of the canopy should be more than about 4" from the lights, with the 2-3" range being desirable. With T12 tube shop lights, you actually can let the plants TOUCH the lights.
With city water if you are not seeing obvious leaf problems you should not have that as the main cause for concern. It's your use of light. Arrange the grow area next time so that you may drop your lights (on chains is good) right down to the canopy and only raise them if you have to. But you should not have to, because you will instead be concentrating on keeping the PLANTS short and flat.
Good luck!