4 Pack Bio-foam Filter Inflatable Lay Z Spa Cartrid 58323 Filters Vi Way 100% New And High QualityColor:BlueQty:4pcsYou are looking at Z type foam filters that are compatible with many models of inflatable hot tubs. Please be warned, you will see many misshaped versions of these filters for around the same price like square or hexagonal. They are this shape because they are cheaply made and obviously not as good fitting as the round types that give a more consistent surface area. they are also unusually thick which obviously restricts water flow putting excessive strain on your pump. Why put a thick hexagonal lump of foam in a housing designed for round filters?I used the original filters myself for approx 12 months and noticed they only lasted around a week. it was almost impossible to clean them. More importantly they were costing me a fortuneI decided to look into a foam alternative and after about 6 months of trial and error I settled on the filters you can see in this listing. I've been using them ever since with no problems at all.These are much cheaper than the original filters, much more free flowing and I find they filter much better.i have managed to source round filters rather than the cheaper misshaped ones that are for sale elsewhere. these will filter water much better due to the consistent surface area and are proven to be a better fit. These filters do require more attention and I recommend using Bromine as this chemical is odourless, cheaper, better for your skin and much more filter friendlyIf you do choose to use Chlorine i strongly recommend changing these filters weeklyPlease note these filters will lose some colour through use.. This is completely normal and is nothing to panic about. other sellers colour their foam green to hide this, however I believe in being completely transparent with my customers