To add to Hive account@connie1018's explanation:

It's not your SP decrease, it is your VP (Voting Power).
If you would like a more graphical illustration, steemworld.org/@honjun88 would be a neater choice.

Looking at your account, because your SP is so low, it yields no effect on your voting. You only contributed a "thumbs up", while you are not helping the reader neither yourself (curation) in the long run.

Therefore, Connie's summary on the need to Power up and her illustration is very important for newbies like you. :)