# Starting ppm using reverse osmosis

**URL:** <https://ilgmforum.com/t/starting-ppm-using-reverse-osmosis/120709>\
**Category:** Preparations\
**Created:** [October 17, 2025, 10:08pm UTC](https://ilgmforum.com/t/starting-ppm-using-reverse-osmosis/120709 "2025-10-17T22:08:13Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Olddude916](https://avatars.discourse-cdn.com/v4/letter/o/e9a140/32.png) [@Olddude916](https://ilgmforum.com/u/Olddude916)\
**Post date:** [October 17, 2025, 10:08pm UTC](https://ilgmforum.com/t/starting-ppm-using-reverse-osmosis/120709/1 "2025-10-17T22:08:13Z")

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So…. I use reverse osmosis water for my tank. Question is- after draining the tank there is usually a little left in the tank. My water comes in at zero ppm, once in tank,that still has a little bit left, ppm is about 50ppm. Do you count that 50 for total ppm or do you deduct that? Thanks.

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**Author:** ![Riskguy](https://sea2.discourse-cdn.com/growingmarijuana/user_avatar/ilgmforum.com/riskguy/32/884243_2.png) [@Riskguy](https://ilgmforum.com/u/Riskguy)\
**Post date:** [October 18, 2025, 12:31am UTC](https://ilgmforum.com/t/starting-ppm-using-reverse-osmosis/120709/2 "2025-10-18T00:31:39Z")

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I do not count the 50 ppm…technically you are supposed to…but I do not believe it has a great affect on results.

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**Author:** ![MidwestGuy](https://sea2.discourse-cdn.com/growingmarijuana/user_avatar/ilgmforum.com/midwestguy/32/914277_2.png) [@MidwestGuy](https://ilgmforum.com/u/MidwestGuy)\
**Post date:** [October 18, 2025, 7:51am UTC](https://ilgmforum.com/t/starting-ppm-using-reverse-osmosis/120709/3 "2025-10-18T07:51:30Z")

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Any reading at or below 50 PPM can be ignored.

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**Author:** ![1HappyPappy](https://sea2.discourse-cdn.com/growingmarijuana/user_avatar/ilgmforum.com/1happypappy/32/580108_2.png) [@1HappyPappy](https://ilgmforum.com/u/1HappyPappy)\
**Post date:** [October 18, 2025, 1:30pm UTC](https://ilgmforum.com/t/starting-ppm-using-reverse-osmosis/120709/4 "2025-10-18T13:30:27Z")

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I agree with the others.  
I use my tap for dwc, autopots, and soil on the rare occasion i use soil.

My tap is around 100-120ppm and i just ignore it.  
If i want a 300ppm mix then I know the reading will be 400ppm.

I will note that for my dwc plants i do use store bought distilled water to pop them and get them started in rockwool cubes.  
But once they get roots and ready to go into a bucket, they get the tap water mix.

These are all i have growing atm and I’ve neglected them all week so i got a little ph drift atm and they will get adjusted today and these deficiencies issues will clear up.

 ![17607939541948543689711634258057](https://global.discourse-cdn.com/growingmarijuana/original/4X/a/8/9/a898374df56187d014a46de11229f376f487040b.jpeg)  
 ![1760794001764716121719307822846](https://global.discourse-cdn.com/growingmarijuana/original/4X/a/b/d/abd9df8e49d649307dd470513b7ae0a279e37374.jpeg)

I usually have a lot more going but this summer was a rough one for me and I wasn’t able to keep up and work at the same time.

But now that winter is over, I’m excited to fill my big tent up with autopots 😅