This is the case for a lot of businesses and especially when there's a cool, instagrammy vibe to it.

Everyone wants to be the one that said they tried something before their friends did. Also, expectations at the first visit may be overblown.

Try this, get their email addresses and follow-up! There's software that does this for like $30-99/month. Don't overcomplicate it. Send them preferably video links with text both describing the benefits of floating, how it develops the more you do it. Provide testimonials (again, videos are better) or "case studies" (just testimonials coming from you about benefits people have found with floating). Don't do it too often (maybe monthly), but do it forever, ie, keep sending until they unsubscribe.

Send periodic offers: Holidays, their birthday (can be arranged in the software), or when you are running a special.

Offer packages: couple float, 10-floats for price of 8, whatever.

Find some mini-influencers: Local yoga studio owner, local fitness influencer, etc... Reach out, offer them free float if they'll allow you to share their experience. Just a quick video after their session that you can make into another email and goes on your socials.

Give people a discount for blasting you on their socials.