Replacing my 75 g reef tank with a 90g tank, do I need to keep my old water?

[davids1024]

I am replacing my 75 g reef tank with a 90g tank, do I need to keep my old water? I would perfer to set up my new tank (different location in house) with all new water. I am moving all my live rock and livestock with the exception of the crushed coral bed, I am replacing that with a 2 inch sand bed. One reason I do not want to keep my old water other than the inconvenience is it is fairly high in nitrates (70ppm) and phospahates.

[Falko]

IMO. You will need to keep your old water. If you move the fish offer to the new tank with much lower Nitrates. It will shock them. And might lead to the loss of your fish and livestock. If you really want to do a complete water change. Run your new tank for at least 2 weeks. With some LR in it. And then you will need to slowly adjust the old tanks water, by means of doing water replacements every few days. 10% every second day would be a good rate IMO. You will need to do this to bring down the Nitrate levels in your old tank. But I don’t think that it makes sense to do so. Remember your Sand bed served as bio filtration. If you replace all your water, and all your sand. What will filter the new tanks water except the LR.

[Entropy]

I would keep at least some of it. The problem is all your livestock is used to (maybe no happy with, but used to) the water you have now. If you swap it to zero nitrate water I think you might lose some livestock. At least be ultra careful acclimating them to the new setup. Basically treat them like newly acquired livestock. Water changes will get rid of you nitrate problem, or if not IMO you will soon have the problem again. Are you overfeeding?

[fishdr]

do not keep your old water. People with nano tanks routinely to 100% water changes. As long as the ph, temperature and salinity match with the old water you will be fine.

Why would a fish need dirty water??? if you were used to poluted air and you suddenly moved to the country where the air is fresh, would you need time to adjust???

[Entropy]

He is not doing a 100% water change though, he is doing a complete water change, removing his substrate, and moving all of his tank contents. Right off the bat he is losing his substrate and all of its bacteria, as well as anything growing on the glass of the old tank. So basically he will be relying completely on his live rock for filtration which should be fine, but IMO taking at least some of the old water would allow the fish to adjust easier.

And to answer your air question, IMO yes you would need time to adjust from polluted air to fresh.

[davids1024]

I am having a hard time understanding how my fish will be stressed with all new RO/DI 0 nitrate/phosphate water. To say they will be stressed to go from high nitrates to low nitrates just because they are used to it does not really make sense to me.

I was more concerned about loosing beneficial bacteria, I wanted to know if all new water would cause a significant bacteria reduction, I do not want a ammonia,nitrite spike

[Entropy]

The bulk of your bacteria loss will be from losing the substrate and glass surface IMO. You will not have any die off IMO, or an ammonia spike, so if you are not concerned about the fish, I wouldn't worry about anything.

My logic on the fish is that if your fish have adapted to the high nitrates, and their bodies are used to the way the water is, changing to 100% fresh water may be a shock to them. Fishes bodies have to adapt to new conditions including water quality and chemical make up, every time you move them from tank to tank. If this were not the case, all you would have to do is make sure the water was the same temp, salinity, and PH and you could just dump them in. It is your call, but I would treat this as a new arrival, and acclimate them accordingly.