Short answer bud... Its the reactor design. I ran 4 reactors up to this point, 3 worked well and never had issues with unsteady flow that constantly slowed down... One did. After trying everything to try to troubleshoot the one... Came down to design flaws to me regarding pressure.
Some say you can run a prefilter for the CaRX but that didn't work for me either. So really, get an old PM CaRX, a Korallin, or an MTC Pro Cal and you can ditch the peristaltic pumps.
Otherwise, run a peristaltic or be ready to kick up your flow every 7-10 days when it slows down again. Just my 2 cents from the reactors I've played with.