Aha.....this is the thread.....popped up in an email....
My opinion on heavy water changes is this....
You can do 75% changes. I wouldn't say every week. You can do it if ya do it correctly. Usually to correct an imbalance in the tank. Otherwise, if you must, 25% is enough. We know how much I do and how often...haha.
For the disagreements......
There are a handful of folks here, well intentioned I am sure, who are stuck in their experiences, and are like hammers looking at nails sticking up in a.deck. Sometimes it takes a while to get these folks out of their shells. It is hard.to remember that we are across a globe. Various experiences. Various issues. Some new, some old schoolers. We need to keep an open mind to others ideas. Sometimes, what you don't see anything wrong with, will rub someone the wrong way. Friction is.good. It creates education. But there is no need for name calling. Even the guys firing.up their BBQ's in their living rooms. Nature will handle them. There is no reason to try and subvert natural selection in those cases. We can only hope they are talkin a gas grill and they have a window cracked open, or they will win the darwin.award. Calling them idiots will serve nothing more than ones own ego.
Also....it is quite.difficult to read words on a.screen how they are intended to land without inflection. What could be an innocent jab attempt at comedy may land.on the other screen as hostility. Now, we cannot be held liable for someone elses gig, but, we can all remember to take what we read with a grain. So long as someone isn't directly firing at you, with obvious ill intent, well, it's sill to get upset on the internet. It's not like anyone is gonna.step out and.discuss it like adults eh?
Don't be silly folks.
Change out yer water however you want. They your fishies. Like Colin said, you'll know you have an issue when you are filling the tank. Been there, done that. It happens pretty quickly. I suspect if you can do a 20% without issue, you will be fine, so long as you temp match the water. That is the crucial part. Don't add 75% cold or hot water directly to the tank. Get a meat thermometer and temp match the tank, use dechlorinator if ya want or need depending, and make sure the water fills slow and.maintains tank temp, and all should be ok. Also....be on the lookout for micro bubbles. These will kill your fish too. It stops the gills from working.
Moderators are capable of that as well 
