Hi stratis and welcome to the forum.
First check if you have one shot or top up redex. One shot will say put everything in, top up will say put 50ml or similar in at each refuel. Don't put all of the top up in at one time. If you have top up you can use it as per instructions after you have used a one shot treatment.
In general terms:
Redex and STP are budget end additives, they will clean, but won't get you back to new. STP do a dual pack valve and injector clean kit for about £10.
Forte is used by the trade and can be difficult to source, see link in alfanige,s post.
I used powerboost from www.ecotekplc.com/power_boost.htm on mine and you can also get 10k boost or other similar products from halfords or motor shops.
Dave.
Marea 2.0 20v
FIATcentral window sticker
Blue gaiters
Blue sidelights
Blue interior lights
Blue lacquer on engine
Feeling blue

Ecotek fitted, removed and waiting for warm weather
So much to do, so little time.... and Totally Skint!!
