It also depends if it is a busy clinic where you will be doing back to back treatments all day, or if the hourly rate applies if you are there, even if you are not doing treatments.
70% of one treatment per day is not much, 6.25x8 and only doing one treatment is OK, 6.25 for one treatment and no pay for the rest of the day is low.
Figure out what you think you are worth, let the spa charge what they want, if you start thinking They're making too much money off me, it's easy to get resentful, but the spa can have huge expenses, receptionist, cleaner, fit out, product, ect (I know of one spa using Pevonia, the cost of the prodct for one of the facials was 35% of the treatment cost, their therapists got 50% leaving 15% for the spa, most of the other treatment product charges were much less, but it gives you an idea of how what the spa can be paying that you don't know about). Find out if you are meant to be washing linen for free the rest of the day, or if you get the 6.25 for that, or if you are only meant to do the treatments. Are you meant to be supplying anything?