So glad I found this forum. Hopefully someone can answer my question.

We´ve bought a brand new spa for our 9 year old daughter, who is physically and mentally disabled. She really enjoys being in the spa with the jets and blowers on, Led lighting, waterfall and aroma therapy.

We´ve had the spa for about an week and a half now and I have a question about the water level. But first the spa details:

Sunbelt Ultra Wave
2 x 2.5 hp pumps
3 kW heater
7' 11" x 7' 11" x 37"
525 gallons
Spa temperature is set to 37° C, which is 98,6° Fahrenheit.
Two filter cycles per day of 6 hours each.
Tha spa has an ozonater
The spa is equipped with a bromine system (our daugther will drink from the water when she gets a chance, so we must use as less chemicals as possible)
The spa is raised about 5 inches with some free space underneath, so we can use our person lifter (sort of forklift) to move our daughter into the spa.
The spa is located indoor, room is heated and has glass from floor to ceiling on 3 sides and doorway to bathroom on the fourth side.

During installation, the spa was filled with water up to the level indicator. As the spa experience is new to our family, we have used it on a daily basis for about 1.5 - 2 hours. Much more than we eventually will, but that´s how it goes with new things.
After about a week, I had to top off the water level. It had dropped about 1 cm (0.4 inch) below the indicator. I keep track of the water level now on a daily basis and see it is slowly dropping. I don´t believe the spa has a leak for two reasons:

- it´s brand new and the company I bought it watertests all spas they get from Sunbelt.
- the spa is located indoor on a floor with bathroom tiles. Any water leakage would show on the floor immediately.

I´d really appreciate some data on water level statistics. I understand the water level will lower over time (hot water, steamed up windows, people getting in and out, etc). But what is normal for a spa with these dimensions, settings and use?
I don´t mind topping off the spa every now and then. But I would like a confirmation that 0.4" under these circumstances is normal. If it is, I must get some extra bromine because with topping off at some point the bromine level will become unsufficient which will reflect on the water chemistry.

Any advice is highly appreciated!