Remineralizing Ro Water


Prolific Poster
Apr 7, 2010
Kingsburg, CA
My well water parameters are:
PH = 8.3
KH = 17
GH = 15-16
Ammonia = 0
Nitrites = 0
Nitrates = 50 to 60 ppm
TDS = 750

My neighbor gave me a calcium filter which lowers my TDS to 350. I do not know what effect it has on my PH, KH & GH.
I have a new (not set up yet) RO unit (without DI) dedicated to my fish room.
I would prefer to remineralize RO water with tap water? (Guessing 75 to 80% RO will provide nice water with nitrates around 10 to 15%) I don’t believe my well water has anything harmful in it as the garden does really well.

-Do I need to add any products like Seachem Equilibrium or a GH booster, or both? Or would I just add Potassium, Phosphate and Plantex CSM+B?
-Should I not use well water to remineralize and use above products and add nitrates?

Thanks for the help


New Member
Sep 16, 2018
75% RO water will give you KH and GH around 3-4, for KH this is good, but I would add some GH booster to reach GH around 6.


Lifetime Member
Lifetime Member
Jul 13, 2017
Arnold, MD
Too big of a variable with the RO water.
Set up the unit and report the findings.

I use RODI and the water is zero for everything.
GH Booster is cheap stuff and easy to adjust for any level.
KH can be low .5 - 2 dKH would be fine.


Lifetime Members
Lifetime Member
Jan 6, 2016
Like many things in this hobby, much depends on the goals for you tank.

If you are going low light low tech, your well water parameters are probably fine. A mix with RO water even better.

If you are shooting for a high light high tech tank with more demanding plants, you would probably be better off going 100% RO and settings all parameters where you want them.

As to KH, personally I dose my RO water to just under 2 dKH, no issues at all keeping pH steady.

If you do go with pure RO, you can easily set GH & KH with MgSO4, CaSO4, and K2CO3.

If you blend it with tap, no way to tell what you need without measuring your levels. GH is mostly a combination of Ca/Mg. You can get a Calcium kit to measure Ca, then calculate Mg based on GH.

And again, how involved you want to get depends very much on your goals. More difficult species are more sensitive to everything. Many easy to grow common plants aren't too picky at all.
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