KH is a buffer for pH.
KH of only 1 degree is so soft the pH can be almost anything at all; other things in the water like organic acids or CO2 will control the pH.
I would raise the KH to about 3 degrees and see what that does to the pH. Add carbonates. Potassium bicarbonate, or sodium bicarbonate (baking soda) are the most common materials.
I would read the labels on the products you have. If any contain carbonates use that. Use it in small doses and make sure you allow it to dissolve before you test the result. You could dissolve it in a small jar of water and pour it into the tank, then test after it has circulated.
Yes, people who use pure RO usually adjust it. They might blend it with tap water and the tap water supplies the minerals.They might add minerals in the form of GH booster and a source of carbonates.
Pure RO does not have the minerals that plants and animals need.
The ways they adjust it depend on the livestock.
Soft water fish: Add a GH booster and a source of carbonates so the GH and KH are between 3-5 degrees. (research the exact value if you will be keeping or breeding something wild or delicate)
Hard water fish: Add GH booster and a source of carbonates so the GH and KH are between 10-20 degrees. (Again, research the fish you want to keep to determine optimum levels).
Nitrifying bacteria need the carbon from carbonates. If the KH is too low they do not grow well. They need a little bit of other minerals, too. While I am cycling a tank I keep the GH and KH about 10 degrees, and add some plant fertilizer (KH2PO4) and micros. The pH in a tank I am cycling will be well into the upper 7s.
The scientists who study these organisms keep them in even harder, more alkaline water.
This is OK while you are cycling the tank, then a big water change when you are ready to add fish can be adjusted so the water is suitable for soft water fish, if that is what you are going to keep in the tank. While you are growing the bacteria (cycling the tank) you want them to grow fast. Provide optimum conditions to grow. After the population is big you can alter the water because it is OK if they are not growing and reproducing so fast. Just enough to keep up with the fish population. And plants are helping with biofiltration.
Chemistry was not my strong suit
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