My tax return lowered by $2,000 after adding my second T4. I still make under $30,000 a year. What happened?

My tax return was estimated to be around $2,300 but dropped to $300 after claiming my second T4. I make under $30,000 a year but I was taxed heavily on my second T4. I live in Alberta but even last year with the same taxes and income, I had over $2000 return. What happened to change that?