Why don't you ADD an additional reactor or other type of diffusor so you have two?
It seems like you are almost there so maybe you just need to get 'over the hump' so to speak.
Can you add a DIY PVC reactor or another AM1000 and maybe power it with a 400-500 gph pump? You can have this outlet run from the opposite side of the tank.
Maybe run either of the reactors with a needle wheel pump to help break up the c02?
Maybe direct the current c02 flow more from the bottom so it has longer dwell time in the tank?
Yes a week is sometimes not enough time to see differences. You should see it soon though........
Another powerhead may help, but I found that I needed less flow when my c02 diffusion method was improved. Most likely won't hurt, but another reactor/pump will also increase flow........
Hope this helps.