Your earned merit won't be deducted when you send a merit to someone else. The only thing that will be deducted is your smerit. For every merit you received you also receive 0.5 smerit therefore when you receive 2 merits then you will also have 1 smerit. It's better to send your smerit than to hoard it as it is useless if you only keep it and never sent to other forum members who deserves it.