Quick update..
My rain water is Fine..mid 6's ph..
BUT...
I dont really get any.
Last season was an anomoly..most of the world got odd weather last year.
Tap water is 8.4 ph..which is right on the end of the safe to drink scale.
Bottled water is 8..which was a shock...
But..
in summer I use 30-50 ltrs per days...so I couldn't afford to run them on bottled anyway.
I have been using the ph down to buffer the water.
AND..
been bubbling.
This gave me less build up..
BUT..
still by 6-8 weeks I could see the damage.
I THINK it is calcium build up.
We are in the highest calcium area in Spain.
I dont think that the vinegar will harm a thing
I'll run with the vinegar..I don't have options..I want to germ tomorrow..
To get 40 ltrs of water down to ph..mid 6...took around 3/4 qrts of a Pint of white vinegar..
but it is relatively cheap..so we will see how it goes.
Nothing like a live experiment..
I've only done watering ph ATM...
the compo is ph balanced..
But..
measuring the run off is my next step.
I'll let you know.