Ruint2

I bought a 12 gallon fish tank about 3 weeks ago to rescue 2 fish. I have never owned a tank before. I now own 4 to 5 inch Pacu in this little tank. The previous owner bought them from a large super store that had them labeled as silver dollars. If I can get them well I plan of finding them a better suitable home. The first week and half or so I over feed the fish per fish food instruction. Now only once every other day (per chain pet store).

I have a low alkalinity level 0
and acidic water 6.2
I bought pH increaser today, new filter, and added some salt (per local pet store)
This made the fish freaky (i.e. swimming up and down, in to wall continuously, breathing hard) so, I did a 1/3 water change, added chlorine eliminator, and bio stabilizer.

My ?'s are:
Can additives be added all at the same time or should they be added in at increments if so, what are they?
Can salt act as an anti-bacterial or should I buy something for this white film problem which is also on uneaten food and clouded the water?
Is this white stuff fungal or bacterial the tank only gets artificial light.
How often should bottom tank gunk be vacuumed? I have yet to do so

If there is something I need more detail about in order for an answer let me know.

Thanks to all..
Ruint2

Ruint2

The salt seems to have had a good effect on the white film. The cloudy water is not as bad either. Still working on getting the Ph and the acidity at the correct level. Going to post these fish on Craig's List of Atlanta for a new home in a few days if all is well with them.

The fish are not acting freaky any more. Hope someone out there can help with my other ?'s or would want these fish if in local area.

Thanks to all for looking...
Ruint2