Tap + R/O mix - The Planted Tank Forum
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post #1 of 6 (permalink) Old 10-27-2015, 09:11 PM Thread Starter
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Tap + R/O mix

My water is very hard (350ppm CaCO3, 500ppm TDS) and I just ordered a 6 stage RO/DI unit. If I wanted to be able to grow soft water plants like Rotala Macrandra, what ratio would be good? I want to ideally have a GH and KH of below 4.

Something like 10/1 RO to Tap? Should I just experiment and take it from there, measuring my GH/KH along the way?

Any help is much appreciated. So much to learn!

Also, since my tank is currently filled with tap water, would my first few water changes be pure RO/DI? Or should I just stick to the ratio I come up with.

Last edited by sl3xx; 10-27-2015 at 09:57 PM. Reason: adding second question regarding transition to RO/DI from tap water in the tank
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post #2 of 6 (permalink) Old 10-28-2015, 02:30 AM
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My wild guess would be 4:1, but you should experiment to find out.
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post #3 of 6 (permalink) Old 10-28-2015, 02:42 AM
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Your target is 4dGH. 4dGH * 17.8 = 71.2ppm

Tap water GH = 350ppm.

350 / 71.2 = 4.91.

So you need 4.91 parts RO to 1 part tap.

Don't hit the tank with that ratio though. Take things slowly. 2 parts tap to 1 part RO for first water change, 1 part tap to 1 part RO for next water change, 1 part tap to 2 parts RO for next WC.......you get the hint.

If patience isn't your strongest virtue, do the water changes every other day, or every day until you get GH to where you want it.
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post #4 of 6 (permalink) Old 10-28-2015, 03:17 AM Thread Starter
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perfect information, Audionut. Thank you!
And thank you Argus.

I really want to be able to grow Rotala Macrandra since it would look amazing in my tank, as well as Rotala wallichii. The Macrandra I was growing had great looking top 3 inches, but then as time went on the lower leaves grew translucent and started to melt. I hope I can grow it in softer water.

I think I'll do a W/C every other day or every third day until I get to that level. I usually do a 40% weekly, should I stick to 40% each time I do these transitional W/C? Or stick to smaller changes until it's the right GH/KH?
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post #5 of 6 (permalink) Old 10-28-2015, 03:47 AM
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The important part is not changing the mineral levels in the tank by large margins, quickly.

40% will be fine as long as you slowly mix in increasing levels of RO with the tap water. You can mix in larger amounts of RO with the tap water, and perform smaller percentages of water change for the same result.

Little bits of RO with lots of bits of tap, large water changes.
Lots of bits of RO with little bits of tap, small water changes.
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post #6 of 6 (permalink) Old 10-28-2015, 04:24 AM Thread Starter
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Thank you.
I'll do this schedule with 30% of my tank's water ( 4 gallons )

Day 1 ------------ 2 gallon Tap __ 2 gallon RO
Day 2 ------------ 1.5 gallon Tap __ 2.5 gallon RO
Day 3 ------------ 1 gallon Tap __ 3 gallon RO
Day 4 ------------ .66 gallon Tap __ 3.33 gallon RO - End Ratio

Last edited by sl3xx; 10-30-2015 at 07:58 AM. Reason: changed numbers to 4 gallon WC
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