How Much Percentage Water Change Allowed?

So I keep hearing Rainbow fish loves a huge water change. Brings up two questions to my mind. #1 how big of a change is legit?
#2 can we do a big water change if the tank is cycled? (Mine is cycled)

 

100% WC's are fine, as long as they're done correctly. Your cycle won't be impacted.

You'd just have to:

Catch all of the fish, and put them into buckets of their old tank water.
Drain the tank.
Do all of your cleaning (I'd suggest to do all of your major tank maintenance here).
Re-fill the tank.
Get the water to temperature.
Re-acclimate your fish into the tank as if they were new.
Done.

You won't want to do that weekly or anything, but a 100% WC is beneficial IMO. Maybe do it every 6-12 months. Some will disagree, but this is a hobby of opinions.

I do 50% weekly, on most tanks.

 

I just do 50% water changes weekly. I see no need to perform a 100% water change. You'd be better off doing back to back water changes than removing the fish and doing a 100% water change.

 

I do 50% weekly as well. I don't have rainbows yet, but I do plan on some before too long.

 

I do 50% weekly as well. I don't have rainbows yet, but I do plan on some before too long.

You should!! I discovered them pretty late...they are one of the intelligent species...they can actually monitor what's going on outside the tank.

 

I usually do about 50% weekly and I've done 75% several times sequentially once when I had to deal with ich or high nitrates.

 

So I keep hearing Rainbow fish loves a huge water change. Brings up two questions to my mind. #1 how big of a change is legit?
#2 can we do a big water change if the tank is cycled? (Mine is cycled)

Hello SSJ...

Work up to the point you change at least half the tank water every few days and you'll have no tank problems. You don't need to do anything else to keep a healthy tank.

Old

 

Every successful aquarist establishes their own personal routine and sticks with it as much as possible.
As for me, I perform two 30% water changes weekly (Mondays and Fridays).
I make an exception at vacation time (2 weeks per year) and if Monday or Friday falls on a major holiday like Christmas or New Year's Day. Otherwise, it's a routine I stick with religiously.
That routine works for me, my plants, and my fish.
I have never performed a 100% water change on my tanks and I would consider doing so only as a last resort in an emergency situation.

 

I make an exception at vacation time (2 weeks per year) and if Monday or Friday falls on a major holiday like Christmas or New Year's Day.

And you call yourself a fish keeper!

 

I agree with OLD.

My water changes vary from tank to tank depending onstocking levels. In several I do 9+ gallons out of a 20 gallon tank, more than 50% when you subtract substrate, 2Xs a week. But all get at least one 50% change a week.

And not wanting to jinx myself but no diease in 9 months, 7 tanks.

IMO water changes are the key to fishy health.

 

I would suggest Aprox 50% water change. If you do more than that make sure temp and ph of new water is Aprox same as tank water to avoid big swings on your perameters. You can do as big of water changes as you want without it affecting your cycle. The bacteria doesn’t live in the water, almost all in filter with only some in substrate/decor

 

Hello again...

It takes several days for enough fish waste material to dissolve in the water to the point that the fish are affected. By simply removing most of the old tank water every few days you remove most of the dissolved waste before it builds up and whatever is left in the tank is diluted in all the new water. There's no need to do any math or other calculations. Simply change out most of the water weekly.

Old

 

He's not changing the water to keep water params perfect, he's already got that I believe. I think he's asking how big of a water change is safe to do with his rainbows as they love large water changes, like the spring rains coming in. You could easily do 75%. Just make sure temp is the same and ph is roughly the same.