As an earlier poster said, the following is all being said from a place of concern and not over-criticality.
Accepting a $20k disparity in cash flow from the market is a luxury in and of itself...a luxury that your tenants are currently benefitting from...not you. In fact, the biggest winner in these circumstances is your "AirBnB tenant" who is probably growing their profit margin because their biggest expense is locked and under market. (What good fortune!)
I definitely understand the point about not wanting to lose good tenants but let's frame it differently: how many of us property owners would pay a tenant to simply stay put and not move? Under normal circumstances, probably not many. However, in this case that's exactly what you're doing to the tune of a cumulative total $20k you are just gifting to them. Moreover, when you're so far under market...you leave yourself vulnerable to the impact of an insurance increase or a tax reassessment by Hillsborough County. At that point you will be scrambling to find a way to make the numbers work. This is no way to live as a property owner! :)
Lastly, I realize that the Tampa markets have seen crazy appreciation but nothing is forever. The longer you are under market, the less attractive your property will be in the open market to other investors. Pricing investment properties can be a tricky thing but if you are 35% under market rent you are more than likely only going to be approached with "bargain"offers should you choose to sell. So by not raising the rent, not only have you lost recurring cash flow, you also risk losing money when you sell what could be seen as a less profitable asset.
I agree with Nathan G. That type of rent increase is just realistically not something that will go over clean with existing tenants without lingering issues. Every tenant is different but in most cases it's just best to run out the existing leases, clean it up, and re-market. If you are worried about the quality of tenant, there are plenty of services and resources available that can help or even take over that process for you. You're already losing $20k (of real money) so having to do some turnover repairs shouldn't dissuade you so much that you need to continue to prolong the shortfall. Wish you luck!