Try giving it distilled water only. You might need to flush it with lots of distilled water, to get out the rust, extra iron or calcium from the hard water and alleviate the lockout.
And get the tools to test, they really are not expensive. That would help with knowing exactly what to do or what to add to correct the problem.
Here is a really affordable TDS meter on amazon:
Here is a really affordable pH meter with a lot of high ratings by customers.
http://www.amazon.com/Etekcity-Accuracy-Pocket-Handheld-Tester/dp/B00FJFEB2O/?tag=greenrel-20
Here are the drops:
http://www.amazon.com/General-Hydroponics-Test-Kit-1-Ounce/dp/B000BT32UA/?tag=greenrel-20
And strips:
You can try e-bay as well. But simple paper test strips like these can often be found many places easily like at drug stores or hardware stores. Also many swimming pool pH test kits can be used.
Hope these help.
~MacG