We have a rain water tank but I had always thought the water wouldn't be suitable. I am always used it for water changes on the marine tanks, the turtle tank & the tropical fish tanks, but for some reason I got it into my head that it wouldn't be ok for the shrimp. RO would be best I aggree. If i could find one like you mentioned at around $100 that my budget could handle. I have one fairly new tank, started 3months ago, with active shrimp soil that I intend to house my mischlings in, but have yet to put any shrimp in it as I was waiting for levels to stabilise. It's only been the last few weeks that the ammonia has dropped away, took ages. I have a couple of endler guppies in it now, eating micro pests. I used distilled water demineralized with salty shrimp GH to set it up. The TDS in that is higher now than it's ever been too. I was testing levels every few weeks at the start & tds was always around 100 but it's up to 338 when i tested it today 'sigh'. It's like I have this sneaky leprechaun bouncing around at night sprinkling stuff in the tanks. I will do that test with all three substrates & the filter media & see if the levels change. I'll do it in the rain water, it's TDS is 22, GH1, KH0, PH 6.6 Sent from my Elephone P8000 using Shrimp Keepers Forum mobile app