Calculating water parameters using rain water? - The Planted Tank Forum
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post #1 of 4 (permalink) Old 01-09-2017, 11:11 PM Thread Starter
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Calculating water parameters using rain water?

Hi everybody, I'm getting ready to start filling my tank and stocking soon! But before I do that, I need to test the water in my area first. Right now, I'm just using a Brita filter to get rid of most heavy metals, leaving the container sit for 24 hours in front of a fan to (not only keep my room at above 0%humidity but also to) get rid of chlorine, and will neutralize with prime anything else. However, a friend of mine just tested her water, and she said that the GH and KH were so high that they went over her tests parameters...luckily, it's been raining a lot here, so I can collect some rain water to at least figure out what my parameters are before I try to get livestock. For reference, HC 'Cuba' is growing quite well at least DSM wise, as well as some unknown Rotala/Ammania species. But how do I go about figuring out pH and GH using rain water to reduce pH and GH to testable levels? I know that you can do this...but I can't for the life of me remember how to do so....

Oh, and additionally, can I add driftwood and carbon to the sitting water to bring the pH and GH even down harder while keeping the water clear? If so, how long should I let it sit?

So many fish to keep, not enough aquaria.
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post #2 of 4 (permalink) Old 01-09-2017, 11:41 PM
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This is all my experience using rain water. As always, your results might vary.

Rainwater is basically free RO/DI water with a few caveats:
1) It's acidic due to the dissolved carbon dioxide forming carbonic acid in the rain droplets. If you live in an industrial area it CAN also dissolve sulfur and nitrogen compounds and become even more acidic (i.e. acid rain). Mine's generally around a pH of 6
2) It's chemistry may be changed by your collection method. Mine comes off an asphalt roof into a food-grade 55 gallon barrel. TDS of about 10 ppm.
3) There CAN be stuff in the atmosphere. It's a PITA, but I try to only collect water in the rain barrel after it's rained for about 20 minutes. That way it'll wash out pollen, pollution, and other particulates.
4) Rain is super-soft. kH and gH should be zero or very close. You'll need to ADD minerals to make it plant and fish friendly. I use baking soda for kH and Green Leaf Aquarium's gH booster.
5) My rain barrel is currently frozen solid, and will be for at least a week. Hard to do a water change now.
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post #3 of 4 (permalink) Old 01-09-2017, 11:53 PM
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how do I go about figuring out pH and GH using rain water to reduce pH and GH to testable levels?
Someone correct me if I'm wrong, but I think you'd add it (or RO water--keep in mind the differences that @Method noted between the two) to a sample of your water and then add the proportional number of drops to test that sample. Like, 5mL tap (or tank) plus 5mL RO and test with a metric of 2 drops per degree GH (assuming your test kit uses 5mL test samples and 1 drop/degree). You can go larger as well (ex. 15ml total solution and 3 drops/degree). I'm not entirely positive about this, though so uh, wait for a second opinion I think. I think you might be able to do this without mixing with RO, just using larger straight tap or tank samples...?
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post #4 of 4 (permalink) Old 01-10-2017, 12:10 AM
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First: Get a liquid test kit

Second: Find out what your tap water parameters are

Third: Figure out if you need to make any changes to your tap water. This may include mixing with RO/DI/Rain water *OR* remineralizing with a product to raise minerals in the water.
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