Water softener/toilet/shower

[TvrTone]

Hi

We seem to have a problem and I cannot get my head round it.

A couple of weeks ago, we had a water softener fitted. All seems fine, except we have now noticed that the pressure from the shower seems less, and when we have a shower, it causes the 3 toilets in the house to constantly run. The toilets also run if a tap is left running for more than a few minutes.If I shut of the water supply to the toilets, the pressure than returns to the shower. I will obviously get the plumber back to look at it, but I curious as to what was it causing it.

Any thoughts?

Thanks

Tony