Homemade RO watermaker

Hmmm

Preservative is usually antibacterial/antimicrobial and keeps membrane damp and in good shape.

When a unit is sitting it usually is bio fouling... in optimum conditions (optimum for bacteria that is) they can double every 20 to 30 minutes....
Think 1,2,4,8,16,32,64,128,256,512 and so on....
Older membranes were cellulose acetate, they worked well but had 2 issues. Higher pressures needed and bacteria could eat them. But could handle small amounts of chlorine.
I believe the newer membranes are polymide...originally could not handle any chlorine. But had higher flows with lower pressures. And bacteria found them less edible.

As far as the stainless or plastic...yup.
Keep in mind stainless can do weird things in anoxic environments. As without oxygen it has no protection. Additionally and here I show some ignorance...I dont know the flouride ppm in seawater, but I do know that a local facility used stainless housing in RO membranes to remove arsenic and fluoride. They spent more on stainless cause it seemed a better choice. 8 months later their system looked like a sprinkler system due to so many corrosion holes burnt in it. They had to buy new pressure vessels and piping in PVC to replace the stainless. Why....that's the interesting part. Flouride when concentrated (which occurs in reverse osmosis) strips the nickel out of stainless and it then corrodes like mad.

So I would suggest plastic over stainless...will cost less and cause less issues.

 

Thanks for the info Sean !