Tip #1: When my partner and I steam-cleaned carpets professionally for five years, whenever we occasionally ran out of the special cleaner we simply substituted a very SMALL amount of Wisk laundry detergent. Use ONLY a small amount or you'll have more suds than you care to deal with! I'd imagine this same product would work with a carpet shampooer.
Tip #2: I have used this combination for years and it works well. One part lemon ammonia to 4 parts hot water. You might want to try in a test area first. Good luck!
Tip #3: I have a friend who swears by Oxy-clean in the carpet cleaner. I have only tried it on spots. The problem with most carpet cleaners is that if you don't get all the soap out then after the carpet dries it will attract more dirt and every time you shampoo you will have to shampoo sooner again. Since oxy-clean is not a "soap" this shouldn't happen.
Tip #4: I have very successfully used Wisk Laundry Detergent in my
carpet shampoo, and for really bad stains I've added some liquid Oxy.
With regards to the sudding problem mentioned in one of the tips my
advice is two-fold. Firstly remember that by its nature a carpet cleaner
will create sudsing, so you don't need to use much detergent.
Secondly, I add vinegar or a fabric softener liquid to my solution as
well, which drastically reduces suds and prevents your carpets from
becoming static laden which is also a bonus. My preference is vinegar as
if you use too much fabric softener your carpet may get dirtier faster
and vinegar is cheaper and works just as well.
I'm very hesitant about Tip 2 as ammonia is something that causes
breathing difficulties for many people. My experience comes from living in
a home with white carpets and furniture as well as toddlers and dogs!
I've had many friends ask me my secret to keeping my carpets so clean...D
Tip #5: Reduce suds in your carpet shampooer by placing a small piece
of handsoap in the water take up tank. The hand soap stops the carpet
shampoo from foaming...KrisAn