Water changes

[marie]

I'm mostly just curious but everytime someone has problems with their tank and water changes are recommended they are told never change more then a 10%-20%.
Every water change on my smaller tanks (50g), I change out 50% and never had any problems what so ever. I'm not even that precise in matching salinity although it is usually close.

How many people have actually had bad things happen if they do a large, say 50% or more water change? I don't mean when the bad batches of salt were around or when you are changing salt brands. I mean regular everyday water changes, when you've used salt from the bucket before and know what the cal/alk is.

A large water change makes so much more sense when you are having issues and yet everyone recommends lots of smaller changes which takes twice as much new salt water to reach the same goal

I think I should of made this into a poll

[Pier Pressure]

We change about 30% out of our 28 gallon once per week and we have a fairly large bioload. We did lose a batch of fish overnight once but the corals and inverts were okay so we still aren't sure what that was about. Some kind of weird spike. No other problems and everything seems healthy. We have had this tank up and running since November of 2006.

[justinl]

i always recommend (and do) weekly to biweekly 20% changes. it's just so that you're not drastically changing your params in a very short span of time. for example, i dont bother heating my water before a change, so a large change could bring down my temp really fast. salinity might change too if your not careful with top off. etc etc.

i think there is a more safety in smaller more frequent changes, rather than the larger infrequent changes (which would cause more stress during the change process). while it is on the large-ish side, i dont think 50% is really big... 75% would qualify though. 100% is a definite no no in my books.

during emergencies, large cahnges dont always make the most sense. I agree that sometimes it's a good idea, but certainly not always. especially if you're not really even sure what the problem is. a 30% change during those times, i think is enough most of the time just to give you time to figure out what your problem is.

[marie]

Originally Posted by justinl

during emergencies, large cahnges dont always make the most sense. I agree that sometimes it's a good idea, but certainly not always. especially if you're not really even sure what the problem is. a 30% change during those times, i think is enough most of the time just to give you time to figure out what your problem is.

I think I disagree with that, unless you pick up a bad bucket of salt (which can happen) I can't think of any problems that can't be solved with a large water change. (I'm not talking about hitchhiker crabs, aiptasia, fireworms or the like kind of problems)

Edit, Ok I lied I just thought of one instance and that is starving corals

[Quagmire]

I do 50% weekly water changes and have never had a problem.I try to match salinity,temp and buffer my alk couple dkh higher, ph is usually close .But they are never an exact match.The only problem I can think of when doing a large emergency w/c,as long as parameters are in order might be light shock due to better light penetration in clean water.Think of the ocean,an area the size of our tanks get a 100% w\c numerous times a day.

[justinl]

well unless you have already identified the problem, i think the problem with the large changes, given that the new water is good and temperature matched as well, is that something will be changed drastically... and not necessarily something you can/do test for. there's so many things that might be off taht we just cant account for... we dont even know the complete chemical composition of real seawater. while a large change can be good, it's not something to be done blindly or regularly imo. if you do know what the problem is, then yes, act accordingly.

yes i agree that a large change can solve quite a few problems, but most times, the aquarist doesnt know what the problem is (which is my point), and there are inherrent risks in a large change itself. i suppose it's a balance thing. does the risk outweight the benefit, or vice versa? i dont think we can generalize that.

Q, yes, a single area of a few gallons in the ocean does get a 100% change many times a day, but that is not a rational comparison due to scale. it's like taking a look at one cubic centimeter of our tank and saying, that it gets 100% water change numerous times a day within our tank. but a change with what? the same water that was previously occupying it. so really, nothing changes. i suppose you could say the ocean is a small tank with a near infinitely large sump... which obviously cant compare to a closed system tank.

[marie]

yes i agree that a large change can solve quite a few problems, but most times, the aquarist doesnt know what the problem is (which is my point), and there are inherrent risks in a large change itself. i suppose it's a balance thing. does the risk outweight the benefit, or vice versa? i dont think we can generalize that.

But what are the inherent risks exactly and are corals stressed by a large water change (other then being out of the water for awhile which happens in the ocean at low tide all the time anyway).
If you are using the same salt that you always use and the salinity and temp are matched you should be good to go.

This is what I'm curious about, has anyone done a large water change, stressed their corals to the point of dying and can definitely say it was the water change that did it?

[Rippin]

One other thing to add to the mix - if you change in the range of +40%, then many of your corals that are near the top are out of water. For a short time, this does not pose a problem, but if you're slow to refill would this cause added stress? Especially if the water change was initiated by a problem? I would think that with such large water changes the MH lights are turned off so that it doesn't cook the corals at the top.

[marie]

Originally Posted by Rippin

One other thing to add to the mix - if you change in the range of +40%, then many of your corals that are near the top are out of water. For a short time, this does not pose a problem, but if you're slow to refill would this cause added stress? Especially if the water change was initiated by a problem? I would think that with such large water changes the MH lights are turned off so that it doesn't cook the corals at the top.

There are corals in the ocean that spend a few hours out of the water at low tide they get cooked by the sun and rained on, but yes If I'm going to be more then half an hour then i will turn the MH lights off

[Quagmire]

Originally Posted by justinl

Q, yes, a single area of a few gallons in the ocean does get a 100% change many times a day, but that is not a rational comparison due to scale. it's like taking a look at one cubic centimeter of our tank and saying, that it gets 100% water change numerous times a day within our tank. but a change with what? the same water that was previously occupying it. so really, nothing changes. i suppose you could say the ocean is a small tank with a near infinitely large sump... which obviously cant compare to a closed system tank.

I don't think the comparison is off at all,assuming you have parameters in check.Say in the ocean a clam dies,the current replaces the foul water around the clam which dilutes and dissipates.Althogh the replacement water come from the same body of water,it is fresh and clean,where as the old water was foul.If you are using the same salt,mixed to the salinity,at the same temp and PH,for a water change,then it is no different than what is in your tank,only fresh.
I'm not saying the w\c will fix the problem,if the above dead clam was in a tank you would have to get it out or the tank would foul again.
But the w\c in itself won't cause a problem,aside from the possible light shock mentioned in my first post.