Sorry Wilkesy but you are near fully stocked already. What kind of monitoring have you been doing to know what your water parameters are? They can change very quickly, and not to the good, with a new tank. When I see 35 litres I think 10 gallons because it's the units I'm used to. The thumb rule for fish is one inch of adult fish, not counting fins, for each gallon. You are within an inch or two of that value right now. In the mean time your tank will never "mature". What will happen is that a bacterial colony will become established in your filter that can convert the ammonia your fish are producing into nitrites. That is both good and bad. It is good to get rid of the ammonia but the nitrites are also toxic. A second type of bacteria will become established that can process nitrites into nitrates. That is only good. It is how you get a much less toxic chemical into your water in place of the nitrites and ammonia. There is a link in my signature that goes to a place where they talk about fish-in cycling which is what you are doing.
Until you have a chance to read up on it and get the needed test equipment, your best bet would be daily 30% water changes. I know that sounds like a lot of water but the 10 litres you change could mean the difference between life and death for your present fish. Once you are testing, you can guide the water changes by the results of your chemical tests instead of just doing large daily changes. Once you are testing and understand what you are doing, you will change water as needed to reduce ammonia and ntrites to less than 0.25 ppm. Once your cycle is complete you can back off to only change water as needed to keep nitrates to less than 40 ppm. That might be an every other week water change, it will depend on your fish loading.
