Gitlab Selfhosted Server size increase very fast

Hello dear Gitlab-CE Community,

I have a question to the Gitlab selfhosted server. I have installed gitlab at first in 04.01.2019 and the server size was around 1GB. Now i have repos with a complete size of 450 - 600mb imported from my github but the server size is in my opinion way to high. The size is at the moment around 17/18 GB. Is there a comment or so how i can clean it up? I already used apt-get clean to clean-up the cache but its still the size 17/18. Also check the folder where the apt-get clean is proceeded and this is empty. I hope that you guys can help me.

Good Regards, cRUSHERHLG