Mining amount reduces

[Haz218]

I am a beginner so I don't know much about mining but I've tried the bitcoin ever mine site. First it icreased my BTC slowly but suddently I discovered my total amount reducing. The number went down during time so I closed the site. Then when I begun again it started increasing again. I mined as much I could and my total amount was about 0,004 BTC but when I loged in next time it was down on 0,003 BTC.

So my question is...
Is there some explanation why this site behaves like this or is the site only messing up with me and what if I invest on hashflare, will it be a risk this site will have the same behavior? I was thinking about invest some on hashflare to mine even more but when there's always a risk it will reduce instead of increase I'm very doubtfull doing it.