Spa Fitter
Hydropool Hot Tubs Serenity 5900 Replacement Cover
The Hydropool Hot Tubs Serenity 5900 takes the AIRCAP 1™ Medium — a foam-free replacement hot tub cover for square spas 86"–88". The Serenity 5900's cabinet measures 85.5" x 85.5", inside the Medium's range. The cover weighs 35–40 lb for life, costs $1,195, is engineered to comply with ASTM F1346-23, and carries a 3-year limited warranty.
| Spa cabinet | 85.5" x 85.5" |
|---|---|
| AIRCAP 1™ size | Medium fits 86"–88" |
| Cover weight | 35–40 lb — constant for life |
| Price | $1,195, free US shipping |
| Skirt | Ziptech™ modular, three lengths included |
| Safety | Engineered to comply with ASTM F1346-23 |
| Warranty | 3-year limited warranty |
Why the Medium fits the Serenity 5900
The AIRCAP 1™ comes in six sizes covering square spas from 77" to 94". Each size is built to overhang its band slightly — that is how a spa cover is meant to sit — so the Medium, which fits cabinets 86"–88", covers the Serenity 5900's 85.5" x 85.5" shell with the right overhang. Instead of a rigid foam core wrapped in vinyl, the AIRCAP 1™ uses welded drop-stitch construction (the material of premium inflatable paddleboards): a sealed air chamber that cannot absorb water, so it never becomes the waterlogged, two-person lift that ends most foam covers.
Cabinet dimensions can change between model years. Before ordering, measure your Serenity 5900 side to side across the top of the cabinet in both directions — the SureFit™ guide walks through it in two measurements. If your spa measures between two sizes, round up.
A 85.5" x 85.5" footprint rounds up to 86" × 86", and every spa we list at that measurement is on one page: hot tubs that take an 86" × 86" cover — the same AIRCAP 1™ Medium, at the same price.
Other Hydropool Hot Tubs models we fit
Not a Serenity 5900?
The Spa Fitter matches 496 models across 40 brands to the right AIRCAP 1™ — or measure any square spa with SureFit™.