Spa Help

Hi folks,
I have recently inherited a Spa/Hot Tub with the house I just moved into. It's an older (around 10 years) fiberglass/acrlic octagoanl tub. The heater and motor aren't beneath the tub. They're actually in my basement. I don't know the brand of tub.... The pump is a Heyward and the heater assembly seems to be a Arra (if that means anything to anyone) universal 6000.
The problem that I'm having is that I can't get all the bubbles to work. There is a jet on 7 of the 8 sides (the stairs don't have a jet), and two sides have two jets. There is one master jet that if you turn it on it stops the flow to all the other jets. The master jet works just great, it blasts all sorts of air and water. When I turn off the master, the flow from that jet doesn't seem to be stopped completely. I can' get at most 4 of the remaining jets to shoot bubbles. The amount of bubbles from each depends on which of the jets is on and which is off. Some only work if all the others are off, some are more forgiving.
I think that I might have a problem with pressure because one of the jets, even if all others are off, just seems to sputter air and not provide a constant flow. The other reason that I think there may be a pressure problem is that the return doesn't seem to be sucking very hard. I was under the impression that if you stuck your hand over the return in the footwell it would be somewhat more difficult to remove it. That isn't the case.
I appoligze for the longevity of this post, but I try to provide as much info as possible.
Thanks, Matt

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