decksandspas

First off I would test whether it's the heater or like you said you could test the pumps circulation. To test the heat use a multimeter and place positive and negative probes on each side of the connections to the heater element (while the spa is powered on). If the heater is receiving 220volts it should be just fine. To test the pumps circulation remove the filters and place your hand over the filter intake to see if you can feel any suction. After you've tested both these things you can also test the sensors by placing the multimeter on them while the pump is running and while it is not running (while set to "ohms") it should have no resistance.

How often are you currently using shock?

You could stand to increase your Total Alkalinity a little bit, generally I recommend around the 80ppm range. Your pH is just fine at 7.5. However, having your alkalinity at the 50ppm level that you had it at should not be the cause of your pumps leaking. You stated you have had the spa for less than a year and I personally have never seen a somewhat low TA level causing any problems with the pumps even over a greater period a time. With soft water, low alkalinity and high bromine/chlorine levels I have seen damage done to the pumps but this is seems to be a different scenario (unless the bleach is really overdosing your fcl). I would check the connections to your pumps and find our exactly where this leak is coming from. I would guess you're looking at a connection or gasket that is loose or kinked and not corrosion or chemical damage. Remember if the chemical methods you were using with your old spa are the same ones you are using now there should be now difference. Essentially all the spa companies use the same pumps, packs and plumbing.