Why is my water becoming so soft?

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gobygoby

Aquarium Advice Newbie
Joined
Aug 31, 2011
Messages
1
Hello!
I'm currently having a problem I've never had before and am looking for advice. I've searched all over the internet and have not found a similar situation, I'm hoping someone here will be able to help.
I'm getting back into CO2 injection so I'm much more concerned about the KH and pH of the water in that tank. Out of the tap, it has a pH of 7.4 and a KH of 3.5, which would work well. But the water in the tank has a pH of 6.7 and a hardness of around 1 KH.
I did a 30% water change, with little to no effect. I waited a few days and did another 30% water change, still no effect. Then I added 5mL of Reef complete, waited a day, still no change. I've done that twice more but still no change. Finially, I added a tiny bit of baking soda and after one day I've been able to keep the hardness at 2 KH and the pH has risen to 6.8, but with all that I've done, the hardness and pH should be much closer to the original tap water 7.4 pH and 3.5 KH. Something is eating up all my hardness.
At first, I figured it was the malaysian trumpet snails that seemed to be multiplying. I didn't mind having them in the tank since they didn't eat my plants and they cleaned up the substrate. I pulled out as many as I could find and that didn't solve the problem. I have a little mopani drift wood in the tank, but not much. There aren't many plants in the tank yet, and according to Ca, Mg and CO3 loss Experiment, they don't change hardness levels. I do have a lot of evaporation in this tank and I'm having to top it off every few days, but that should increase hardness, which is what I'm trying to do.
Does anyone have any ideas, suggestions, or have faced this problem before?

Thanks!

Tank info:
18 gallon (tall)
Two bunches of stem plants, one rush
Two baby clown knifes (who will move out when they get bigger)
One black ghost knife
Farlowella, otocinclus, kuhlie loaches
Small amount of mopani driftwood
Two 26w CFLs
Rena xp canister filter connected to under gravel filter
9W UV sterilizer
HOT Magnum Biowheel
 
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