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Transitioning a tank from hard to soft water


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To start off, want to be clear. I’m talking about doing this with an EMPTY tank. No fish will be in the tank during this time.

I’ve got a 20 high that I was previously using to breed swordtails. My water out of the tap is soft and acidic, so I had used crushed coral and seiryu stone to buffer it up.

The swordtails have since been sold off and I’m needing the tank to grow out a spawn of angelfish, who are currently in a tank of straight tap water. I’m sure they would do fine in the harder water, but I don’t want to keep bouncing them back and forth between waters since my LFS has the same soft water.

I’ve removed the crushed coral and the seiryu stone, replaced it with a large piece of mopani wood and done several large water changes(including a close to 100% change today), but my PH and hardness are staying pretty high. 

I’m sure it will probably take some time, but is there anything I should be doing (or not doing) to help the transition along? I have some other driftwood I could throw in there that seems to release a lot of tannins, but I also don’t want to crash things and have to play catch up. Anybody have any experience here?

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Hmm… so: (1) take your tap water, collect in a clean glass measuring pitcher, allow to rest for 24 hrs. (2) test KH and GH on rested water. I’d suggest trying strips and titration drops. Maybe your LFS could help if you only use one method. (3) Now do a 90% water change on your tank, adding dechlorinator as you normally would. Allow it to settle for 24 hrs. (4) test KH and GH on the tank using two methods as well.

If you have removed _all_ of the crushed coral from filters and substrate, I find it hard to believe that this tank would buck your tap water parameters.

Water gets softened as acids slowly build up. Decaying plants, food, etc. cut into water buffer and eventually lower KH. Plants also absorb minerals. Water regains hardness from contact with Rocky substrates, limestone bottoms to river beds, etc. Rainwater is perfectly soft. Often, well water is hard, having filtered through many layers of dirt and stone to the the underground reservoir. 


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