Planaria are flat worms .. they are bad ... I had some I siphioned them out daily .. eventually they were gone .. You can use a product called flat worm exit .. read the directions very carefuly . Have lots of carbon on hand , when they die they can/do release toxins into the H20 column ..
It took me about 3 months to irridicate them from my tank by siphioning ..
10 gallon ~6.5 gallon custom