Tropical Fish Keeping - Aquarium fish care and resources

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stephanieleah 12-22-2009 10:21 AM

Article on Water Changes--where is it?

The article compared large weekly water changes to more frequent smaller water changes.

But now I have another question:

Does doing larger water changes impact the fish's osmoregulatory system? My reason for asking:

I used to do 30% water changes but now I do 40-50% because I am now fully stocked. I was thinking that taking out half the water makes a pretty sudden change in the tank--the bottom layer (ie the one with the most weight on it) is now gone and there's only "lighter" pressure in the tank (for my pleco or loaches, for example, that would be robbing them of their pressure zone pretty suddenly). (Kind of like us going on an airplane and the ear pressure deal).

I started doing a back to back 20-30% WC to 1) lessen the pressure differential during the WC and 2)keep my filter going because right around 30% it can't suck up water and makes a weird noise that's hard on the motor. Does this matter? Does the osmoregulatory function work faster than the rate of the pressure loss during the WC?

aunt kymmie 12-22-2009 10:31 AM

Yes, that info was written up by Byron. I'll go try to find it...

jaysee 12-22-2009 11:18 AM

The difference in pressure between being in 10 inches of water versus 20 inches is miniscule. IMO, for the vast majority of fish, it's not worth worrying about. I've been doing 50% changes for a long time.

1077 12-22-2009 11:44 AM

In my view, it's all about dilution of dissolved organics or total dissolved solids. Performing 20 percent water changes dilutes 20 percent of said solids or organics.Performing 50 percent water changes dilutes 50 percent.
With that said however, IF the tanks water change routine had or has been few and far between,, I would perform two to three 20 percent changes in the course of a week rather than large water changes which would suddenly change the chemistry and indeed affect the osmoregulatory functions of the fish. If one begins doing frequent large changes from the beginning or frequent smaller changes (ie) twice or three times a week ,then the fish will tolerate it more easily than infrequent large water changes.
Some sensitive species do not tolerate even moderate changes that happen suddenly but if the total dissolved solids or organics don't ever have a chance to become excessive by performing 20 or 50 percent changes from the outset, then there is little chance of a problem. It is as mentioned,when water changes are few and far btween that fish struggle with sudden change in chemistry even if it is for the better.
Is why most agree that small frequent water changes are better than large infrequent ones.
I change and always have,,25 percent twice a week and 50 percent on the weekend for a total of three changes each week.

Evan 12-22-2009 11:54 AM

my opion is change as big and as often as possible. as long as the new water you are adding is the same ph, hardness you will be fine with massive 75% plus w/c daily if your bio in the filter can handle it is the question. I do 50-75%w/c daily on my tanks and more on the weekend with no problems. and if ther is a change in anything my fish love it because after w/cs there is always a spawning frenzy. the best thing to do is aireate the water you are putting in the tank for 30minto hr so the ph can settle and never never never age water longer than 24hrs no matter what. because bacteria will build up in the container and give you all kinds of problems. once the ph is settled use it

Twistersmom 12-22-2009 12:01 PM

Here is a good post made by Byron on large water changes.....Post #5

LisaC144 12-22-2009 12:24 PM

This thread is making me think that I need to do more than my 20% pwc weekly.

jaysee 12-22-2009 12:50 PM


Originally Posted by Twistersmom (Post 293234)
Here is a good post made by Byron on large water changes.....Post #5

Good link and a very good post by Byron.

Looking back, there were a couple big turning points in my fishkeeping - When I started overfiltering my tanks and when I started doing weekly 50% waterchanges. The two have made fishkeeping a breeze.

LisaC144 12-22-2009 12:56 PM

I do ove rfilter my tank. I have a filter up to 110 gallons and I have a 55. However, I do not do 50% water changes.

jaysee 12-22-2009 01:29 PM

I'm gonna be honest - I wouldn't be doing weekly 50% changes if I didn't have a python. I also wouldn't have as many tanks :-D

Many of my tanks are very heavily stocked, and since I have no live plants, the large changes are needed to keep toxins down.

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