LFS RO/DI water has higher TDS than SF tap water

[badbread]

Well, hello all. New to the site, saw a bunch of BAR people over at Atlantis aquarium the day of the last frag swap. Wish I knew about the swap before then and hope to attend a swap in the near future.

Just wanted to put out a little warning about a LFS near me (clement street.) No names as I don't know if I can post topics like this but just an FYI, if your familiar with the area I'm sure you can figure it out.

I recently purchased a mightymite RO/DI since lugging jugs back and forth to the LFS is such a PITA. I picked up a TDS meter with my order and decided to test various water sources.

SF Tap water: 35-40ppm
Brita SF tap water: 28 ppm
Waste line from Mightymite: 120ppm
Clean line from Mightymite: 0ppm

RO/DI from this LFS: 90-100ppm

I really don't understand how that is possible, how can the water coming out going into their storage tank be dirtier than SF tap water? Even if the waste line was emptying into the storage tank it couldn't pass the TDS of the source could it? Maybe rain water?

I don't know, just an FYI, I was super pissed off, I didn't test their RO/DI for anything else but maybe I should, might explain the diatom problem I was having.

Thanks

 

[tuberider]

If it's that one place, likely they drain their water changes from their freshwater tanks into their RO

You did the right thing buying your own RO unit

 

[sfsuphysics]

Well the reason the wasteline is dirtier is because its carrying all the garbage from the clean stuff that left.

If your system has a 4:1 reject ratio, that means 4 units of waste water for every unit of clean, that means those 4 units of waste water will be carrying the waste from 5 units of water, so you'll increase your TDS by 20% If you add the calcification and other junk that the waste water is purging from your RO unit you might add a few false readings due to excess ions, so I wouldn't worry too much about your waste water output.

But man I live in SF and would kill for TDS that low, heck if it was that low I'd probably go DI only.