Water Change, all at once or a little bit at a time??

[Whoyah]

I am curious to know what method everyone employs when they do their water change. For ease of conversation, lets say you have a 100 gallon tank and do a 20 gallon water change. Do you:

Option A: Take all 20 gallons out at once and replace with the new 20 gallons.

Option B: Take out a small amount (say 5 gallons) and replace with 5 new gallons. Repeat until new water is gone.

Option C: Something I didn't think of (please explain)

In the past I was an Option A guy but recently I tried Option B. Option A always missed up my levels between my tank and sump. Option B did not give me nearly as many problems.

[Grandmaster_Toad]

i have a 90...so we are pretty close to the 100 mark in your post. So option B is my choice. The tank here gets a 6 gallon change every other week.
Too much at once is baaaaaad for biz. imo
GT

[tileman]

I do a 10 gallon water change every Sunday morning, clean my protein skimmer and change my sock and mag the glass. My corals and fish love me for it. :D I do have way too many fish though and thats why I do it every week.

[dakar]

How about all 3 and/or a combination of them... depends on the situation.

I think you need to look at a couple of other things here, for just general maintenance, yes option B would be the safest bet.

However if you are trying to correct a situation that could pose a serious danger to your critters, say something fell into the tank and the result was 8 fish dying, and ammo jumped to 40ppm and the bio filter can't convert it fast enough, then option A, provided the SG and temp is as close as possible, new water added slowly over the course of a couple hours would be far more benificial at removing the harmful elements from the water column.

Option B in the last example would reduce the nasties by exponentially less, there is some fancy math formula that can demonstrate this if you really like numbers.

For the 55 (just under 100 gals total volume with sump and such) I do a 8-10 gallon change each weekend. I mix up new SW 35 gals at a time, and let it set for at least a week with a heater and PH running 24/7.

Going to have to figure out a much less labor intensive method for the 180, since I can't sump it to the basement....hauling 20 gals each weekend up and down the stairs won't be a lot of fun. WC's for her start this weekend. Not to metntion she evaps almost 5 gals/day right now.

[Whoyah]

Well it looks like Opinion B is the popular choice. My question was directed at routine maintenance more than crisis management, which I whole heartily agree with you, Dakar. Opinion B you may loss a small portion of the new water but I think that is really OK.

[Reptoreef]

I'm on the B wagon... no more than a 20%(20gl) wc each month with a (5gl) each week if really dirty.

[jerryc]

I do a 10% ever other week and change it all at the same time but i don't thank
10% is a large change amounts to 8 gallons for me.

[peregrinus]

i do it all at once never seen ill effects. about 5 gals when ever i get around to it. lol

[Reptoreef]

Ooops... my bad... I'm on the A-Team provided you are speaking of a system larger than 20 gl for a 20 gl water change(like a 75-100gl.