Bubbling but no rise?

So i have two starters, affectionately referred to as "The twins" by my girlfriend and I. Both live in 1L pickle jars (thoroughly cleaned), the lids of which i have punched holes in and then covered said holes loosely with cheesecloth. Im following a method from a book called "Rocky Mountain Cooking", its a very basic AP flour starter, fed twice daily with 1/2 cup water and 3/4 cup AP flour. I started them 5 days ago. The problem I'm having is that while both seem active, they don't seem to rise at all in their jars after feeding. They have a touch of a sort of paint-y smell to them, but they do also smell like sourdough. I would say ive got a little over 500 ml of starter in each jar, and before the feeding i discard a little over half, so i'm essentially doing a 4:2:3 ratio of starter to water to AP flour. Should I be discarding more starter, or adjusting my feeding ratios? Or is it just day 5 and too early to expect them to perform? The cookbook I'm using suggested they should be ready today using this method, I haven't deviated from it at all. I can tell they arent ready, i just want to know how to better care for them.