Mine did the same for a few months as well (started with 12 and went down to 7), but I started feeding them good shrimp food on a better schedule and they perked up and I'm seeing new ones all the time and they're active and healthy.
Jake's food is awesome and I will never feed my shrimp anything else. I feed them his complete veggie Monday and Friday and feed them the pumpkin delight or the calcium plus sticks on Wednesday. I dose excel/flourish complete M/W/F as well for the plants which has never bothered them either.
As long as you're doing the basics (for me at least) and there's nothing obviously out of whack, they just need to acclimate and then you'll start to see them perk up. I feel like a lot of people over react and change things up too quickly trying to figure things out, but again, that's just me.