Diluting tap water with distilled water? - The Planted Tank Forum
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post #1 of 7 (permalink) Old 02-21-2019, 06:32 PM Thread Starter
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Diluting tap water with distilled water?

I am getting plants for my first tank next week and realized my tap water is pretty hard. Shows around 300 ppm by my reading and I wondered if I should dilute with destilled water as I have seen recommended here and other places as well. I want to have betta and ember tetras and otocinclus which I've seen can all handle pretty hard water but wondered about the plants too.

I welcome any experience or suggestions as I am ptetty new and finally getting started on the first tank. If something seems obvious tell me because I probably don't know.
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post #2 of 7 (permalink) Old 02-21-2019, 07:54 PM
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Some plants are peachy with hard water, including Vallisneria. But diluting with deionized water is not unreasonable, particularly if the water is alkaline (high pH) in addition to being hard.
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post #3 of 7 (permalink) Old 02-22-2019, 04:25 AM
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For what it's worth:

I have really hard water (775 ppm TDS out of the tap) and pH 8.2. None of my plants did well, including vals. I needed a crop of duckbit for my goldfish and tried 3 different mixes of tap plus distilled from the store to see what worked best. The 6:1 distilled to tap ratio was definitely the best.

Then bought an $89 portable R/O unit from Amazon and tested a series of mixes, looking for something in the range of 100 ppm TDS and 7-ish pH. Once I got that dialed in, my plants are growing and looking much better.

I keep my Jikin goldfish in straight tap water and they're fine. The Betta, and neocardinia shrimp are ok in their 100 TDS mixed water, but I'm not convinced the nerites are doing well; I just can't tell with them.

My next build will be a pygmy cory tank so it's good practice getting consistent water parameters before I take that on.

Hope that helps?
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post #4 of 7 (permalink) Old 02-22-2019, 02:04 PM Thread Starter
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Well I went home and did some dilutions and it occured to me I read the test wrong and I'm much closer to 150 ppm GH. I think I will be done at this level of hardness as I'll add plants for a while and add fish later so thinga should balance out a bit I think.

Thanks for the quick replies, I appreciate your information and experiences.
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post #5 of 7 (permalink) Old 02-26-2019, 01:17 PM
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I had a hard water situation, so I picked up an RO filter to dilute my tap water.

It has a pretty high gallon rating, and would be a simpler way to dilute your tap water.
No more luging gallons of water from the store.
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post #6 of 7 (permalink) Old 02-26-2019, 11:39 PM
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My water is also liquid rock. Straight from the tap, it reads 8.4ph, 300ppm KH, and 300ppm GH. I really don’t know if that is a true KH or GH reading as that’s the upper limit on my test strips. Despite the high readings I am getting decent to good growth from my plants with what I guess most would call a low tech setup. No fish currently, but as I’d like to get some tetras with a ram (blue or Bolivian) or Apistogramma as a centerpiece, the water conditions are far from ideal. I did some experimenting with different dilutions and at 75% distilled/25% tap I’m getting readings of 6.8pH, 60ppm KH, and 75 ppm GH. As I only have a single 20 gallon aquarium, buying distilled or ro water for weekly water changes wouldn’t be too costly for me. With just plants and snails, would it be an awful idea to remove 75% of my water and replace with distilled or should I do it slowly over a few water changes? Years ago I had multiple aquariums with several different tetra species as well as rams. I never really tested my water parameters back then but I assume they were close to what I have now as most water around here is the same. So I’m not really even sure if I should mess with it at all. Thoughts?
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post #7 of 7 (permalink) Old 03-02-2019, 04:28 AM Thread Starter
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Well in all honesty my tank is more of a walstead inspired tank and so i shouldn't have to do water changes unless i massively replant the tank and do a lot of cleaning or if something goes terribly unexpectedly, so diluting from the start for me is feasible and then tweaking my gh over time with equilibrium if need be. In actuality i used strips to test my water and upon diluting found that my original reading was off and that i am much closer to the 150ppm hardness mark but used a couple gallons of distilled water in the tank upon start up to drop it a tad bit. this is a serious dilemma if you require water changes often, which most people do which is why i think an R/O filter is often suggested. another possible option i can suggest is to put an in line filter in you house somewhere you'd want it and then to test that water and use it in your tank as it would be less hard for sure. Some people put inline filters only to where they get their drinking water in the house so that they aren't filtering water that doesn't mater I.E. toilets.


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