Hi,

This is basically an Academic Question. I have no issues performing Water Changes (WCs). I have 3 setups (soon to be 4) with Semi-Auto WC Systems--so, its not an issue.

In fish-only tanks, from what I understand, WCs are generally performed to maintain a Reasonable amount of Nitrates.

In Plant-Only Tanks: Plants consume Nitrates and , in theory, as long as the nitrate level is maintained at a low, reasonable level (+/-20ppm) there would not be any need for WCs.

This is all Excluding EI, PPC, etc.

I know that this is very Simple theory, but as long as nitrates remain "low"--what is the purpose of WCs? To remove other TDS?

I am just trying to understand what constitutes Water "Quality" beyond the general Nitrification Cycle.....

Again, I wasn't quite sure where to post this, but I thought it might fit in with my other post: "Extending the Nitrification cycle....."

TIA

Speaking only for myself I can say it's out of Pure Laziness !!! I am Waaaaayyy Too Self Absorbed to Test, Monitor, and Maintain the individual components of water chemistry, and Too Guilt Ridden to risk the consquences at the risk of my own wards. Lacking the potential to be an Omnipotent God I am a Diligent Custodian !

Aquatic Life lives, and resperates in that water ! Lock yourself in a closet, Shove a towel under the door, Light a Big Fat Cigar and contemplate the WHY of it all ??? LOL. Prof M

Generally Nitrogen waste, but high levels of trace metals, and salt, etc can also cause issues.

But as long as the plants are removing the N, they also remove the metals, salt etc as well and rather than water changes for export, you now reply on plant pruning/assimilation.

So plants remove everything, not just N waste.

There is still export though........

Regards,
Tom Barr

Thanx, Tom!

That's the explanation that I was looking for......

Bacteria are pretty good really for decomposing, but plants are more general, they take up just about everything, even Gold.

Regards,
Tom Barr

So, for my next idea, I plan to cultivate a big crop of one of our fast growers in a Sierra Nevada stream, harvest it every week, bake it good, separate out the gold, and.............head for Reno to give it back!!

The amount of profit extrracted from Gold trailings is about equal to the cost of processing it.

This is the same old story for most gold mining operations, they need to be profitable, you can get gold , that's not the issue, getting easily extractable gold is quite another.

Regards,
Tom Barr

What about DOCs? Are they also taken up by plants? If not, how are they exported without water changes?

DOC's in natural systems do not keeping rising to extreme concentrations, tannins etc are built up to a certain level and tend to be broken down.

Like NO3, DOC may be decomposed and provide an atmospheric component, CO2 which is assimilated or released the air above, like NO3=> N2 gas.

This is the entire process which wetland wastewater treat relies.
PO4/Fe etc does not have such a component, so plant biomass may be used to sequester it or the wetland soils for rotation with crops for cattle fed, rice etc.

Regards,
Tom Barr

Does this also apply in our tanks (DOCs decompose and aren't an issue)?

I'm a bit puzzled because I had always thought that, in our closed systems (our tanks), there was always some type of waste/organic byproduct that accumulated and needed to be diluted. Ok, in an unplanted African Cichlid tank that "something" would be mainly NO3 but also other organics (DOCs). As a planted tank will remove the NO3 issue, one is still left with the DOCs accumulating... or that's what I had always assumed.

And I thought that this was one of the main reasons that in a low light non-CO2 planted tank a key point was to keep a low bioload. This allowed you to do very infrequent water changes as the low bioload meant less organics...

Or have I got it all wrong?