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Old 12-07-2012, 02:55 AM   #1
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Ratio of RO and tap water?

I've recently moved into a new home, the water is well water and it contains very high nitrates, even straight from the tap. We got an RO system put underneath the kitchen sink and I figured I'd use that for the tank.

However I know RO water won't have all the minerals needed and what not, so what percent of RO should I use? 75%RO/25%Tap? Half and half?


Thank you!!
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Old 12-07-2012, 07:57 AM   #2
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Depends on how high is high.
For example: if the tap has 40ppm then a 50/50 cut would result in 20ppm.

Remember, cutting with RO will also drop the pH. Decide on your mix and then allow a sample to gas out for 24 hours and check the pH.
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Old 12-07-2012, 08:22 AM   #3
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Remember, cutting with RO will also drop the pH. Decide on your mix and then allow a sample to gas out for 24 hours and check the pH.
+1

Another way to determine your mix ratio is see if your LFS will test your tap water dKH (degrees of hardness). If not, API has a test kit for this.... about $10. Your dKH determines the amount of pH buffer in the water, and if it goes below about 4, you run a higher risk of a pH crash. To use mine as an example, my tap has a dKH of 16 and nitrates of 10, so I can run up to 75% / %25 RO to tap to bring my dKH down to 4, and that mix ratio would reduce my nitrates down to 2.5.

On the USGS water map, my region is very hard water, but yours should be softer in Minn. So, for example....... if you have a dKH of about 8 and nitrates of 30, you could go 50% / 50% mix to bring your dKH to 4, which would cut your nitates in half to 15.

Hope this makes sense.....
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Old 12-07-2012, 01:52 PM   #4
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Aww great, thank you for the replies. Just bought the GH KH test kit off eBay, sadly petsmart nor petco has it in stores. I'll also test the nitrate level and see where that stands...
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Old 12-07-2012, 01:53 PM   #5
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Also, RO doesn't need to be dechlorinated right?
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Old 12-07-2012, 02:13 PM   #6
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Also, RO doesn't need to be dechlorinated right?
Not typically no. Depending on the age and efficiency of your filter I would still use some anyway. I have seen RO/DI water with ammonia and nitrite in it if proper maintenance is not performed on the filter unit.
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Old 12-14-2012, 12:34 AM   #7
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Ok, I'm confused about everything that has to do with this test kit. Lets start with this, the KH took maybe 2 drops, for sure 3. The GH it turned green the very first drop? There was no orange to green like the instructions said. And these #s are from the RO water.
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Old 12-14-2012, 07:49 AM   #8
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RO is supposed to be fairly low to zero, that's the point. Now if you cut nasty hard water with it you obtain results as stated above.
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Old 12-14-2012, 12:17 PM   #9
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I have an RO machine and my KH and GH readings are 0, which is the way they should be. Did you get a TDS meter by chance? They come in handy for reading your RO water and will indicate when you need to change your cartridges due to the increase of the Total Dissovled Solids in the RO water.
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Old 12-14-2012, 12:23 PM   #10
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RO is supposed to be fairly low to zero, that's the point. Now if you cut nasty hard water with it you obtain results as stated above.
So how much "pH buffering" is in my RO water based off these results so I know how much I can use? I still have to test nitrates in the tap water...
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Old 12-14-2012, 12:24 PM   #11
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RO water has no Ph buffering in it or from your readings very very little.
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Old 12-14-2012, 12:35 PM   #12
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RO water has no Ph buffering in it or from your readings very very little.
Ok, then what's the point of this test kit? Or is it the tap that I want to test?
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Old 12-14-2012, 12:38 PM   #13
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It's the tap water you want to test.
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Old 12-14-2012, 12:41 PM   #14
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God, no wonder I'm so confused. I'll go test that. Thanks for the help so far everyone...
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Old 12-14-2012, 11:22 PM   #15
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Alright, tap results.

KH 13 drops
GH 3 drops
Tap nitrates 20

Now if someone can tell me where this puts me, obviously I'm too dumb to figure this out myself.
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Old 12-15-2012, 01:03 AM   #16
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If your tap water is 20ppm of nitrates, then using 50% RO to 50% tap (non RO) will give you a reading of 10ppms of nitrate in your tank. This mix will cut your GH down to 1.5 which is getting pretty low and cut your KH down to 7ish since your RO had a bit of KH reading. If you use 75% RO to 25% tap then your nitrates go down to 5ppm, GH down to 0, and KH down to 3-4ish. Which to me is the best readings for the tank HOWEVER with GH of 0 you are going to have to dose MgSO4 magnesium for your plants.
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Old 12-15-2012, 01:08 AM   #17
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Thank you. I don't currently have any plants so that shouldn't be an issue, unless the fish would be missing out on anything of that nature that they need...
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Old 12-15-2012, 01:11 AM   #18
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Thank you. I don't currently have any plants so that shouldn't be an issue, unless the fish would be missing out on anything of that nature that they need...
As long as your not keeping fish like African Cichlids that require hard water then I'd say your good then.
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Old 01-12-2013, 06:32 PM   #19
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I have a brs 75 GPD ro/di filter. I am unsure about the ratio to fill my 2 75 fw fancy goldfish tanks. I do have anacharis. I try to do 50/50
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Old 01-12-2013, 08:50 PM   #20
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You could also use something like SeaChem's Replenish or Equilibrium to replace lost minerals:
Seachem. Replenish
Seachem. Equilibrium
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