RO water or tap water for water change? - The Planted Tank Forum
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post #1 of 7 (permalink) Old 02-08-2017, 11:24 PM Thread Starter
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RO water or tap water for water change?

I started my 15 GAL planted tank about three weeks ago and my LFS said I should be changing out 50% of the water with RO water every other day for the first two weeks, then twice a week for two weeks, then once a week.

I'm starting to learn about fertilizing and am wondering if I should switch over to tap water. I'm sure my water hardness is super low because I've only used RO water.

My City website is pretty unclear about what my hardness is because we have multiple sources, but if I average them it's around 230 ppm CaCO3. Not sure if that's too hard for the planted tank.

Any recommendations on how I should proceed from here on out?

I've attached my city water information for reference.

Tank Information

15 GAL tank
Finnex 24/7 on 24/7 mode
Pressurized CO2 system
HOB Aquaclear 20
Aquasoil substrate
Planted with DHG, Cabomba, Anubias, Alternanthera
No fish yet--hoping to add in a week or two once I get water and fertilizers sorted out
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Last edited by Scottacus; 02-08-2017 at 11:52 PM. Reason: clarity
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post #2 of 7 (permalink) Old 02-11-2017, 03:05 PM
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Using pureRO is not the way to go. Either:

Just use tap water, or blend tap and RO, or use RO and remineralize it.
Since your water appears to be quite hard, you might need to blend or mineralize. But many aquarium plants can adapt to quite hard water, maybe you will be fine with tap.

Plants need Mg and Ca, the main constituents of general hardness.

Hope this helps!

DougN
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post #3 of 7 (permalink) Old 02-11-2017, 04:07 PM
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It seems with the exception of SM water, all the other sources are quite low in GH. So low you would actually have to add some Ca and Mg. It seems the city is constantly mixing the water but we do not know in what %. Do you get a constant KH and GH out of your tap, if so what are they ?

If your KH/GH varies widely then I would go with RO. Its not really a certain GH/KH that shocks the system but an abrupt change.

Most plants can certainly grow in hard water, some do even better. Looking at some of my experimental data, I got 50cm and 85cm total additional length (including side-shoots) over 2 weeks from Myriophyllum sp. "Roraima" at a 14 °dGH ( 222ppm CaCO3) and 6°dKH (104ppm CaCO3) with EI dosing. I would say that high GH/KH certainly was not hurting M. "Roraima". If other lifestock requires softer water (shrimps for example) then adjust to their needs.

PS. I do not know what Alkalinity ppm means ... ppm of what equivalent CaCO3 HCO3 CO3 ?
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post #4 of 7 (permalink) Old 02-12-2017, 10:43 PM Thread Starter
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Thanks for the feedback Doug and dukydaf. Any ideas on how to proceed with a RO/tap blend?

I just tested my GH and KH for tap and tank.

Tank: 71.6 GH, 17.9 KH
Tap: ~250 GH, 143 KH

I'd been using RO water then added a few gallons of tap last week. I just introduced fish yesterday so I'm nervous about changing up the parameters too much. Any advice?
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post #5 of 7 (permalink) Old 02-13-2017, 07:24 PM
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You can easily calculate how much of tap water to mix with your RO to get your desired GH or KH:

In general
cf = (c1*V1+c2*V2)/(V1+V2)
where V1 - volume of tap water, V2 - volume of RO water, C1- GH/KH of tap water, C2- GH/KH of RO water, which is 0, c3- GH of the mix

Because we assume our RO water has 0 GH we can simplify our formula to :

cf=c1*V1/(V1+V2)

I would say target 107-143ppm GH and 53-90ppm KH, no need to be very specific as most freshwater fish are able to adapt to changes, they encounter such differences in nature.
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post #6 of 7 (permalink) Old 02-13-2017, 08:18 PM Thread Starter
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Quote:
Originally Posted by dukydaf View Post

I would say target 107-143ppm GH and 53-90ppm KH, no need to be very specific as most freshwater fish are able to adapt to changes, they encounter such differences in nature.
This is great, I'll crunch the numbers tonight and move toward those targets. Should I proceed slowly, with smaller more frequent water changes? I'm concerned about upsetting the new fish. They were just introduced on Saturday and I'm sure are already having issues acclimating.

It's a 15 GAL tank, I was thinking of doing 3 GAL changes twice a week to start moving in the right direction.
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post #7 of 7 (permalink) Old 02-16-2017, 11:41 PM
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I'm new here and new to actually trying to get a thriving planted tank. I just started using RO/DI and adding a few grams of seachem equallibrium to the 5gal jug to *hopefully* bring the dGH to 4-5 for dwarf baby tears. I got the RO/DI for my saltwater tank so I make the stuff in the garage.

I don't know about freshwater but I know all the other nuetrients, if added to saltwater, cause a huge mess of algae. If not our incoming TDS is 800 and avg hardness is like 270. All that means is more work for filtration...
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