Need help ASAP for Science fair

[deleted-331508]

HI
We were able to successfully complete this project. We have Science fair on Monday.When we did the last trial ,we realised that the pump starts without the conductivity sensor and Potentiometer,and the pump does not stop.After troubleshooting we could concluded that MOSFET may be shorted so we replaced it.IN Radio shack we could only find LM317T and 7812.We are not clear about the terminals .
https://www.sciencebuddies.org/science- ... p040.shtml
The circuit did not work with first MOSFET.With the second MOSFET we tried our best guess for the terminals.The pumped was initially off.After adjusting the potentionmteter,we could normalized by placing both tubes in vinegar.The main problem is after putting the pipes in baking soda and vinegar,the pump did not start by itself in order for baking soda to flow in vinegar to neutralize the solution.Also based on the terminals we guessed ,we also changed the connection based on S,D, and G.
Its due Monday.We can not demonstrate like this.Please help us.Its not possible for us to get same MOSFET at such short notice.Please guide us with the MOSFET terminals and why we are not getting the results.How should we manage ?Also I think we need help with the concept of conductivity sensor.What else can we change?
Please help us ASAP.