Just a word about the water pump you're using. I tried a couple of these pumps out, and they pump very well (good volume and pressure), unfortunately the material used for the gears is rather soft, and as a consequence these pumps do not like to be run dry for even a short length of time. If you do, you will find the gear driven off the motor looses its 'key' and the pump fails. If this pump had brass or composite gears, it would be a superb little unit- pity.
I would recommend running this pump at a lowish speed say 3-4.8 volts, that way if the pump does run dry, the RPM is lower and this should hopefully avoid the above scenario. It should still be pump quick enough or the size of tank needed for a 1/144th kilo!