People will disagree on how much you change water on tank fish all the time. Look at this chart:
You're not safe till you hit day 35.... When you change your tank water, you add a dechlorinator like Prime and that holds the ammonia for 3 or 4 days. My advise is that the first 2 weeks you change 90% of the water every 3-4 days then after that you do 90% 5-6 days. On day 35, your water changes can become weekly at a smaller percentage but in my opinion the fish will get sick if you don't do 90% weekly.
PS: 105 liters = 29 gallons, which means it's good for two gold fish.... Your fish will get sick as they grow. Downsize to two fish or increase the size of the tank.