Are Large Water Changes Killing Fish? Small vs Large Water Changes -

[skjl47]

Hello; This is suggested in the posts so far but let me state it more directly for review.

Large WC done on a regular schedule, say within days and perhaps no more than a week, with care about temperature cause no harm and are a good idea.

If a tank has run a while without a WC then a large WC may be harmful. For example if the tank has had small WC's, 20% or less, say once a week for months or has had no WC for a month or more then it may be that pH differences or other differences from a large WC might trigger sudden problems. At least this is what I have taken from these WC discussions over the last several years.
Such a tank van be eventually gotten up to regular 75% + WC by doing a series of smaller WC say every other day for a while. I guess the math can be had but I do not know it.

I would start with a gradual increase in the WC % every day or three. Say 20% to 25%. Then 25% to 30%. Then 30% to 35% and so on. At least this is how I think about it.

 

[RD.]

I pretty much said all I could in this past discussion on the same topic.

https://www.monsterfishkeepers.com/...tive-effect-on-nitrifying-bacteria-bb.687257/

A couple of highlights from that discussion;

.... under typical conditions, what one might describe as normal - massive water changes are a non issue with one caveat - this should only be done on an established system, with established filters.

This is exactly how I cycle new tanks - 100% fresh tap water (treated with Safe), and an established filter. Done deal, just add filter, instantly cycled and ready for new fish.

Water changes really comes down to bio load, my tanks are all very low in stock, so I only perform them once a week, but when I do it's a big one. The real key IMO is ensuring that the water parameters going in, are very similar as the water going out. In that case, no amount of new water is too much.

For non believers just watch the videos below. My water changes aren't quite that extreme, but close.

 

[Just Toby]

Temp and PH swings should be avoided also if your tank takes 30 mins to refil or more and that means yours sump circulation is off then the bacteria will begin to die without flow.

I would measure the size of water change on need. If your nitrates are under 25ppm doing 20% water change then why do more? If they are not then Do more.

The solution to pollution is dilution.

 

[jaws7777]

Ive had my sumps/filters off for hrs and never had an issue

 

[krichardson]

I'll let you know if anyone snuffs it.

This has been the norm in my water change routine for years.

 

[philipraposo1982]

A big problem is with the lack of understanding with regards to the bacteria in our tanks. Keep in mind that you would have to scrub pretty aggressively to physically remove the bacteria from.its mounted surfaces. No amount of water changes can remove bacteria from surfaces and the bacteria in the water column is negligible.

I do larger weekly water changes and sometimes up to 3 times a week at fin level or slightly above. I always match water temp though.

Those who avoid water changes due to poor quality water out of the tap have a whole other whack of issues to deal with. But to simply avoid water changes to preserve the bacteria is just wrong and has no truth to it.

In addition, to keep TDS levels safe, minerals replenished, nitrates low, and keep the tank from suffering from old tank syndrome aka ph crashing due to acidic condition and therefore your cycle will die off over time. You simply need to replenish a good amount of water regularly.

The tricky part s to find the right balance for your specific aquarium and water supply.

 

[duanes]

I normally change 30% every other day, (in summer when its hot, 30% every day)
This keeps water parameters very stable.
If you change a large amount, but only once per month, you allow nitrate to build, pH to drop and then when there is a water change, the make up water will be drastically different than month old tank water. I believe large water changes, but"infrequently" could be a problem, but the solution is more frequent water changes, rather than less.
I usually have very full 50 or 75 gallon tanks as sumps, and change enough water to bring them down to the pump intakes. That is one reason I like to change water every other day, at minimum.

above one of my planted sumps during a water change.
But lets take nature as an example.
The Amazon river flows at 60 million gallons per second, to me any water changes are nothing compared to that.
Or even the placid Cenotes where I have snorkeled, the flow heading out toward the sea, has beed enough to pull me hard enough to have to grab mangrove roots to keep from being dragged out. That is serious natural water changes.

 

[krichardson]

I normally change 30% every other day, (in summer when its hot, 30% every day).

Duanes,have you set up many new tanks down there yet?

 

[skjl47]

would have to scrub pretty aggressively to physically remove the bacteria from.its mounted surfaces.

to simply avoid water changes to preserve the bacteria is just wrong and has no truth to it.

Hello; I agree with these statements. The bacteria form what is often called a "bio-film" on tank surfaces. I can add a link where this is mentioned later.

I also think where the beneficial bacteria (bb) form colonies has to do with water flow to some degree. The ammonia in a tank with no heaters or filtration seems likely to spread uniformly in the still water by Brownian motion. However the movements of the fish and even a heater should cause some mild flow or at least movement of the water.
Heaters can set up weak currents by convection. I use to set up demonstrations with food coloring to illustrate this.
Even the old style air bubble operated HOB's and in tank filters, UGF and such, would set up some flow.
Back many decades ago I ran a few tanks with no filtration or bubblers at all, just fish and plants. I did not have the test kits back then but the tanks seemed stable so I assume there were bb present.
I guess the point I am getting at is there are bb on many surfaces in a tank. It seems from my reading of posts on this and other forums many think the bb are only on the media of a power filter. I consider that the media is a fine place for the bb to colonize due to the regular flow but that the bb also find many other places to make a bio-film. All the plumbing and surfaces of any power filter for instance.
I suspect the bb will form colonies on most other surfaces. I nearly always place a few snails and live plants into a new tank setup. My thinking being the shells of the snails and the surfaces of live plants can have a few bb colonies. The added advantage of the snails being they should be generating some ammonia by their metabolic processes.
I concede that the greater concentration of bb colonies might be in the filter due to the regular water flow.

Sorry for running on about this.

 

[philipraposo1982]

During big planted tank rescape I have had many times where my filter would be off for hours up to 7-8 hours and never a problem.