I design & build these all the time for places like MIT (a current project) and Cornell. I hope you have a plastic holding tank and plastic pipeing to the system. Otherwise you could be facing more problems in the near future.

Most states require a pH higher than 5.5 and lower than 11.5 for discharge. Do you have state a discharge pemit? What does it say the limits need to be? It would be very odd if you were allowed to discharge a pH limit of 2. That is so low, you are likely to kill off an activated sludge treatment system downstream. The bugs hate large swings in pH, but will tolerate a swing to the high side better than to the low side.

You will need a way mix the tank. It might take two as this is an odd shape. I have used eductors with submersible pumps and have a ratio of 6/1 or so. 1 gallon pushed through the eductor mixes with 6 gallons of tank water. Don't mix NaOH in the piping outside of the tank. The heat can be enough to affect PVC cement. Use thermo welded plastic pipe, socket or butt. A short piece of PP pipe could be adapted to fit the mixing pump, hold a chemical injector in the flow, and end by passing the water through the eductor, increasing overall tank mixing and treatment in one operation.

A pH meter will be needed to control the chemical addition. Need to treat any HF acid? Then you will need a special probe. I might go to a 50% NaOH unless the caustic is free to you. The cost is about the same, but you can treat more water. Test the tank pH and control to that reading. Record by chart recorder the discharge pH so you can allways show regulators you were in compliance.

Send me your e-mail if you want me to supply the controls, components and instructions.