I guess the title asks the question.

Anyone know the differences between Nature2 A vessel models W20034 and W20040?
The internet pictures show they are different.
Something must be different for the extra $70 for the W20040.

(And please spare me the debate on the effectiveness of Nature2. Let's just assume I want to go that route. Thanks.)

TIA

Semi-inground 10K gal
Vinyl
Heated
Tri-chlor (yes I know that debate as well, thx.)