When using any automatic doser it is important that the nutrients and acid/alkali are very dilute. The instructions on many dry powdered nutrients tell you to prepare the stock solutions to quite a concentrated level (100:1 or more). Liquid nutrients are also very concentrated. For a small mixing tank, this will be too strong and even if very short doses are given the system will overshoot. If using powdered nutrient mix them into water so that for each 1Kg of powder you obtain at least 20ltrs of solution. Liquid nutrients should be diluted with water to make up at least 5 times their original volume. Acids and alkalis should be diluted to be less than 2% strength. (if using strong acids, always wear goggles, gloves and add the acid to the water then stir well).
When you have the dilution right you should get a 0.1 mS/cm change in EC when you add around 25ml of A and B stock solutions. In a similar way, the pH should change by about 0.1pH when 25mL of stock solution is added. If it changes by less than this – that is fine but if it changes by more - then you will need to dilute the stock solution further.