Right guys I’ve just tested my before DI (After RO) reading and its 037.
Any ideas on why twinning them up has not saved on resin at all? Sounds to me like I might as well just use the one bigger vessel and keep the smaller one as a spare.
Double di is a 'bandaid' but hasn't addressed the basic problem which you need to address.
Your r/o is only removing 90% of the dissolved solids in your tap water if its 400ppm. Your membrane should be removing 97 to 98% of the dissolved solids in your water leaving you around 12 to polish off. 94% was considered the cutoff point, possibly higher for you because of your high tap water tds.
This basically means your membranes probably need replacing.
Living in a high calcium area doesn't help.
Obviously having good water pressure at the tap is important. You can't just think your water pressure is ok. You have to test it with a pressure guage. Plumbing stores or Screwfix sell them.
The next is to check to see what your pure to waste ratio is when producing water. I'm guessing at your high TDS you would need a ratio of around 3 litres of waste to 1 litre of pure - maybe a bit less waste to 1 litre of pure.
If you are going to replace membranes you must get them from a supplier that sells quality USA made membranes such as Filmtec or Axeon. Cheap Chinese copies look good price wise but don't perform over the long run.
www.daqua.co.uk