Answer:
Any carpet shampoo or carpet cleaning solution that is specifically designed for cleaning carpet should not be hard on carpet. Please know that different manufacturers and formulations may vary from a neutral of pH of 7 up to a very aggressive alkaline cleaner of pH 12.5.
Too much alkalinity left in the carpet (due to improper extraction) may can browning of the carpet fibers and /or rapid re-soiling due to the sticky residue left behind from the carpet residue.