Nitro zorb is a great product too by API if you continue having issues getting it down. The only downside is it'll cloud your tank water. You know this obviously, but that initial nitrate burst you get during the cycle is rough. It sounds like you and Lincoln are getting through it alright though.
I've always found one of the issues with cycling beta tanks is the water flow. With gentler flow your filter cycle rate to be a little lower so your water isn't moving over your filter material as often. I found that it takes a little longer for the cycle to sort itself out in beta tanks, but once it does it's easier to keep in check.