In most spas, when you turn on the jets (which is typically when you are using the spa) only a small amount of the water is going through the filters before re-entering by way of the jet, and the rest of the water is being pulled through one or more by-pass suction fittings usually  located in the footwell area of the spa.  True to the name, this means that this fitting sucks unfiltered water directly back through the pump to be redistributed back out the jets.

However, on a spa with no-by pass filtration you get more filtration when it matters most…when you are using the spa.  That’s because this unique system does not have any by-pass fittings and directly pulls 100% of the water through the filters before re-entering the spa when the jets are turned on.  This means cleaner, clearer water when you are using the hot tub.