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Discussion Starter · #1 ·
Im slowly getting closer to setting up my 75gal. I have to move my 20 to make room. I will be removing as much water as I can to move it but leaving some in tank for the fish. My question is should I keep any of the "old" water for refilling or will fresh water be fine.

I see a lot of people do 50% water changes but Ill be taking at least 75% out to move. So Im worried it would need cycled again with so much new water.
 

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Since most bacteria do not float free but hang on surfaces, the water has little effect on the cycle. It does involve the PH/GH/KH and temperature if you do anything to adjust those.
 

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Not to worry! The VAST majority of nitrifying bacteria live in the substrate, in the filter media, and on plants and hardscape. As long as the water parameters of the new water match the old pretty closely everything will be just fine. Keep some water if you want to, but it is by no means critical.
 

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The water has nothing to do with the cycle - all your bacteria is on the plants, substrate, decor, and filter media.

If your tank water parameters are close to your source water parameters, you should be able to do 75% with no issue.
 

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Discussion Starter · #5 ·
Thanks.
I know that the bacteria was in the media etc. I was worried as to how fast they balance things out again with so much water being removed.
 

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What do you mean 'balance out'?

The bacteria do not mind water changes.

I have done something close to 100% water changes (oops! poor fish were flopping in the low spots in the tank) and there was not even a blip in the nitrogen levels.

I more commonly do 50% water changes with never a problem.

I have moved tanks the way you want to, draining 75% of the water and refilling with new water. Not a problem.

All the posts above are right: There is very little nitrifying bacteria in the water. Do as large a water change as you need to, as long as the GH, KH, TDS, pH are the same.
 

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Discussion Starter · #7 ·
Well its been 24 hrs since move and everyboby is livley and doing well.
Thanks for calming my fears.

Did have a minor setback on new setup. After moveing the 20 gal started to get 75 in place i relized that one of the doors on the stand was ready to fall off. Took it back tonight and they ordered me another one.
 

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It didn't get mentioned until now which is too late but there might be a reason for the idea of old water being important. Not correct but the guy who moves a tank and willy -nilly fills it without much concern is often the guy who also totally cleans his filter and kills all the bacteria in both the tank and filter. Since he doesn't know much about the cycle and bacteria, he may decide it was the new water. WRONG!
 
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