Since there are two bodies of water and they are separate, there should be a separate, not shared filtering system.

Scott

If the spa is higher than the pool, you can run a gravity overflow line from the spa to the pool.

Put the valves half way so both are on at the same time or do the valves have actuators? It might require a little tweaking so the spa doesn't overflow or empty.

Other option is to do a manual water exchange periodically. Manually set the valves for suction on the spa and pool return. The spa will empty into the pool. Then reverse the valves and the opposite will happen. Not automatic but an easy way to exchange the water.

You'll never get them balanced. Plus, the pool needs more than the spa. Splitting them equally will create sanitation and chemical balance issues. It's best to treat them separately.

Scott

I had a seperate spa and pool using the same equipment for years. Adding another 400k heater was not an option as it would have required a bigger gas feed from the street, bigger meter, big $$$$$. The spa had its own booster pump and ozonator and cover. Scott is correct in that its really hard to balance the valves so you can run them at the same time as a slight change in the hydralics will knock it out of balance and dump or overfill the spa. I would periodically dump the spa into the pool and replace it with pool water by manually moving the 3 ways. I found it a lot easier than chemically balancing the small volume of water in the spa. When actuators became available I considered putting them on timers for recirculation but decided it wasn't worth the effort.

The pumps and filter systems can share, just not use the heater at the same time. How would that be any different than an attached spa? A clever plumber could even rig it to so you can do a water drain or exchange between the two for any service needs.

Running two bodies on one system will result is either overflows or running dry. It is inevitable.

Scott

I have managed to get this to work on my own pool and spa but it depends on daily run time. Having a slight overdraw or underdraw can be a problem if you are running 24/7. However, when I did this, it was only for 6 hours per day run time. Since the valves are in partial open for both suction and return, having a few inches of gain or loss per day in the spa is equalized during the period of time when the pump is off. With the pump off and a connected primed channel between the pool and spa, water will seek it's own level via siphoning and the water level in the spa and pool will equalize to the same level. As I said before, it requires some tweaking so you don't have too much under/over flow in the spa but you can get it to work. It works even better if you have a variable or low speed pump where you can run both on the lower speeds.

But again, if you don't want to bother with this then just use the manual swap method.

mystrwizard...we're using a small sump pump and a garden hose to transfer water periodically from our standalone spa to the pool and vice versa. It takes about 30 minutes to do this manually for our 400 gallon spa every 2-3 months or after parties.

This provides fresh water to the spa and saves from draining and re-filling the spa...another benefit...we have a salt water pool and enjoy the salt water in the spa better than un-salted water.

Manually doing this with 3 way valves and a bigger pump like you already have on your pad should make the task faster than my small pump/garden hose approach.

Hope this helps.

As the differential in elevation between the two bodies decreases the problem of balancing the level also decreases. This would also be the case as the gpm decreases. In my case the spa was about 24 inches above the pool which made balancing the levels more difficult. If the OP's spa/pool are close to the same level, Mas's method would work nicely.

I am sticking with what I said. To do otherwise is to raise the risks I pointed to.

Scott