[KatSea]

I know it seems like a stupid question but cant you clean your tank to much?
Can doing a 20% or a 50% water change two or three times a week be bad for the fish and plants? I don't do it but I was just wondering

 

[MMAfish35]

I would say yes, because it can take too much of the bacteria out of the water. If that happens it cause the cycle to start, and if done much can cause the fish to stress out a lot. I'm not an expert, but I would say it is bad.

 

[Nilet699]

The water though contains like zero bacteria. Like 0.0000001% of it.

 

[jentralala]

Depends on the fish. I'm no expert, but I'd say it's unnecessary for most tropical fish (tetras, rasboras, etc), they do just fine with a weekly 30%/50% water change.

It's a whole different ballgame for Discus and Goldfish though. From what I've read about Discus appreciate massive water changes several times a week. And Goldfish are incredibly messy fish with high bioloads that have to be kept in check with large water changes.

 

[jentralala]

Also, for some planted tanks, such as Dutch, they require massive water changes often to replenish the nutrients in the water that come from the tap.

 

[AbbeysDad]

The beneficial bacteria are not water borne as they attach themselves to hardscape - filter elements, substrate and decor. Water changes do not really reduce beneficial bacteria.

Frequent water changes (assuming proper temperature) are not really necessary, but are not harmful as fresh water really can't be too fresh. The only exception might be to begin doing large volume water changes in a neglected tank such that there was a dramatic change in water chemistry that might shock the fish.
Our objective in weekly water changes is to do a volume sufficient enough to dilute the pollution and keep the water fresh. With advanced filtration, proper stock levels, feeding, tank maintenance and sufficient plant life, volumes can be reduced, but WWC's are still required.

As to the question of too clean, I feel it may be possible to clean a filter too much. The filter houses decomposition bacteria that break down detritus as well as BB to process ammonia and nitrites. All bacteria colonies function best when undisturbed. Although we don't want the filter to be neglected, it is beneficial to let it run without disturbance until it's necessary to be cleaned. The time interval varies widely from system to system.

Likewise this is true of the substrate, at least in a planted tank. Again a comprehensive eco-system lives there that functions best when undisturbed. However, it may be necessary under some circumstances, especially the unplanted tank, to aggressively gravel siphon to clean out decaying matter.

 

[MMAfish35]

OK got it, water changes won't hurt bacteria levels.

 

[Byron]

I agree with AbbeyDad's comments. As Dr. Neale Monks wrote in PFK, you really can never change too much water; if you could change 100% of the water every day, the fish would love it. [Assumes basically same parameters, etc.] But this is a lot of work.

The crucial point though is regularity and constancy. The water quality changes a lot in a fish tank, from day to day. So the water change should be regular--once a week for most of us works well--and change enough water to achieve maximum benefit. This will actually work to keep the water more stable week to week. Ad hoc changes can cause considerable fluctuation, as AD pointed out.

You might find this article helpful:
http://www.tropicalfishkeeping.com/freshwater-articles/regular-partial-water-changes-117205/

Sometimes the source water can make this difficult, but assuming your tap water is not adding excessive toxins you are OK.

Byron.