To resolve these problems, go to Edit → Editor Options and look under "General Options", under the "General Options" node, where there are several options related to tab stops. Unchecking "Auto indent" and "Tab to next column" will make the step size consistent. Unchecking "Insert TABs into text for TAB characters" and "Insert mixture of tab/space for optimal fill" will make TOAD use spaces instead of Tabs, which will prevent any problems where TOAD's tab stop difference is different from another program's.
The tab stop distance can also be set at the bottom of this page. Edit → Editor Options → General Options → Display Options → "Show control characters" lets you see where tabs or spaces are used.
To get rid of existing tabs, open your file and press "Replace". Check "Regular expressions". Choose to find "\t" and replace with "\s\s\s" to replace all tabs in the file with 3 spaces. Select Entire and press Replace All.