Lowering GH/KH: Do I need to treat rainwater before using? - The Planted Tank Forum
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post #1 of 3 (permalink) Old 12-26-2018, 04:52 PM Thread Starter
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Lowering GH/KH: Do I need to treat rainwater before using?

I've recently set up a 5.5 gallon aquarium, currently low tech planted but unstocked. My water here is VERY hard. Using the API test kit my GH is 200ppm (11 drops) and my KH is 400ppm (22 drops). I am wanting to breed cherry shrimp and know I need to adjust my parameters a bit before getting them. I'm thinking of using rain water. Do I need to do anything to it before using it such as use Prime, etc? Other than using RO water or rain water, what are my other options for lowering GH and KH?

Edit: my Ph is also high (8.4) so I'm hoping it will help with this also.
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post #2 of 3 (permalink) Old 12-26-2018, 06:14 PM
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Most fertilizers will not work at a PH of 8.4. So you do need to lower the PH. High ph makes most of the iron in fertilizers insoluble and unavailable to plants.

You do not have to use Prime or other water conditioners sine the water has no chlorine in it. Although it might be advisable to use a UV sterilizer to kill any bugs or that may be living in collected Rain water.Getting enough rain water can be an issue. Aquariums do best with one water change per week. Usually I change 50% of the water once a week (I use RO water, rain water is not available). With rain water you either need to collect enough from your roof to last several months or have a source of RO water on hand to handle the dry spells between storms.

As to GH you need to increase it because rain and RO water has no calcium, magnesium sulfur and potassium. Without those minerals most animals will not do well (especially shrimp). Use a sulfate GH boster such as sachem equilibrium or the GH booster available at nilocg.com. Rain and RO water also has none of the minerals plants need to grow such as nitrogen, phosphate, iron and others. So use a good all in in fertilizer will also supply those minerals. Most people Keep GH between 4 and 6. I tend to keep my GH between 3 and 4.

KH helps to stabilize PH by neutralizing any acids that my be generated as plants consume nutrients. You can use baking soda to increase KH. I would only add enough to keep your PH between 6 and 7. That range is ideal for most fertilizers. If you go above 7 you will start to loss iron in your fertilizer.

For a 5.5 gallon aquarium it is generally very difficult to do a low tech setup with RO or rain water because plants will quickly consume all the CO2 in the tank. People often add CO2 from a pressurized tank to do this. or use a product like Seachem Excel to provide organic carbon many plants can use instead of CO2. CO2 or Exile will reduce your PH but as long as it doesn't drop below 6 you will be OK.
The only other option is to overstock the aquarium so the fish produce enough CO2 for the plants. But this can stress fish and also create ammonia and nitrite problems in the tank. Ammonia and nitrite are toxic to fish. Use the smallest fish (adult size) available or make it shrimp aquarium.
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post #3 of 3 (permalink) Old 12-27-2018, 03:03 AM
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My recommendation - use RO water to cut it, not rain water. Rain collects dust and potentially harmful smog if you live in a city, and that's before it hits a surface.

You can also use peat moss to lower KH which will also reduce pH, but it stains water with tannins. Not the worst thing for shrimp as it does have bacteria inhibiting properties.
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