This Must Be Wrong

[gizmo001i]

Hi,
I just read this on a magazine website, in the tips section. Surely this bit of advice is very wrong as a complete water change would stress out the fish involved. Please correct me if I'm wrong, but surely a 50% water change is the maximum that you want to do unless it is an emergency. Here is the article I'm talking about. The comment I disagree with is at the end of the short article:

Tip of the Month:

How do you catch a cichlid in a tank full of rocks without disassembling the entire structure, or a marine fish in a reef tank without removing all the live rock? Easy! Couple the project with a massive water change.

Drain the water until there is only an inch or less left in the tank. It should then be an easy matter to net the target from a puddle of water. Then just refill the tank. (With a marine tank you might want to save some of the water in clean vessels or extra tank, but any tank, fresh or salt, will greatly benefit from a complete water change.

Surely a fish magazine should be giving better advice than this.

 

[Bignose]

So long as you match the water temperature, pH, and hardness of the replacement water, there is very little wrong with doing as large of a water change as you can handle. Now, the fish may get stressed out in that inch of water, but the quality of the water wont matter.

There are only two real occurances when large water changes should not be done. 1) if you root around in your undergravel filter when taking the wster out. You might accidently disturb too much of your beneficial bacteria, and get a mini-cycle. 2) if the tank has been neglected, and there is ammonia present with low pH. If the new water will have higher pH and probably higher hardness, the ammonia-ammonium equilibrium could be shifted towards the more lethal ammonia with the new water. Very small but very frequent water changes are needed in this case.

However, again, so long as you match parameters, and don't do something silly like let your filter dry out, you can do as large of a water change as needed.

 

[andywg]

As Bignose said, changing large amounts of water has no real downfall, though with marine tanks you have the problems of exposing the live rock (that is often the main filter) to the air and the possibility of drying out. I am sure it could be done on SW, but there are more things to watch (temperature, ammonia, nitrite, nitrate, pH, KH, Calcium and phosphates are the ones I can think of off the top of my head) and I would feel far less comfortable changing such large amounts of a reef tank.

I have often drained FW tanks down extremely low to catch occupants and move them out (especially when moving tanks around). The important thing is to make sure that the filter media has a supply of oxygenated water, preferably with an ammonia source.

 

[gizmo001i]

OK, I was wrong lol. I just thought it wasn't such a good idea, but have been proven wrong ( I will eat my hat this evening ). Thanks for putting me right guys.
Ian