I don't know about 'deionized' water, sounds like snakeoil.
Your problem may indeed be old extract, but I would guess it's more than likely you aren't giving it enough time to become the beer you want it to be. Doesn't matter how long you keep it in the primary if you dump it before it's carbonated and conditioned. Flavor changes through all the stages. What starts out as unpalatable, can become fantastic.
I've used old extract, and unless it's from a can, the only problem I've had with old extract is that it is darker than normal, and ends up a little sweeter. Not sour.
I wouldn't think you need to add any kind of salts to the water though, extract contains that already.
And yes, I had a several batches that came out not so good, but improved dramatically after several months in the bottle. Time is your friend here, don't be so impatient.
Your problem may indeed be old extract, but I would guess it's more than likely you aren't giving it enough time to become the beer you want it to be. Doesn't matter how long you keep it in the primary if you dump it before it's carbonated and conditioned. Flavor changes through all the stages. What starts out as unpalatable, can become fantastic.
I've used old extract, and unless it's from a can, the only problem I've had with old extract is that it is darker than normal, and ends up a little sweeter. Not sour.
I wouldn't think you need to add any kind of salts to the water though, extract contains that already.
And yes, I had a several batches that came out not so good, but improved dramatically after several months in the bottle. Time is your friend here, don't be so impatient.