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Discussion Starter · #1 ·
Okay, so animals metabolism produces certain organic acids which combine with minerals in the water to produce, 'organic salts'. I suspect this results in the water increasing in salinity and TDS slowly over time???

And do plants, or any plants, absorb these organic salts? And therefore to keep the water from increasing in salinity and TDS over time the trimmings of plants could be removed from the system to export these salts back out to maintain ecological stablity/homeostasis?

(I want to do a low-tech low-maintenance tank but am worried about salinity & TDS accumulating in an unhealthy manner, but suspect most of these 'organic salts' are what serve directly as fertilizer for plants?
 

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Even with a low tech low maintenance tank, your still going to make at least some water changes.

That will do all you need to maintain the TDS and salinity where you want them. I don't think you have anything to worry about.
 

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Just do not over feed the fish, and things ought to be in a reasonable enough balance that a few water changes will be plenty to keep the excess minerals under control.

And yes, most plants will take in more minerals and fertilizers that are available. Not all the different ones, but many.
Then you trim the plants and remove the minerals that are in those leaves.
 

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Discussion Starter · #5 ·
Okay, let's hypothetically just say that I didn't intend to ever do any water changes, but had an auto-top-off to which I could add minerals/buffer to keep the alkalinity and pH from crashing. Or at least that I wanted to ensure the water quality was kept entirely pristine, without the buildup of some perhaps nasty detrimental organic salts?

Dilution through water changes is one way to deal with it obviously, but not entirely as direct and effective as I'd prefer.

Wiping or rinsing Mangrove leaves, while it might work, would of course not be that efficient a way.

However, if say some fast growing floating plants would tend to uptake those organic salts from the water then those would be easy enough to cull regularly to export these salts.
 

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I've gone about 8 months without a water change, the issue and why I did one was not related to water quality. In fact, that;'s VERY rare that I do that for even high growth rate tanks.

The issues are dirt and trimming and the need to get into the tank, keep it looking good. A water change is just a simple way to fix that.
Several folks and a client have gone 1-2 years without a water change/s.
Is it wise? Probably not, but depends on what look you are after.

Floating water sprite would be an easy way to export and leave a % left to regrow, say go from 10-20, up to 50% before you prune/remove some, then prune back to 10-20% and repeat.
I do this for ponds with several plant species.
 

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Discussion Starter · #7 ·
Thanks, but... the root question here is whether a plant like Water Sprite would absorb all the organic salts and TDS which are a byproduct of biological processes, please?
 

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And the answer is something thats as low tech as what you seem to be wanting will generlly be low in the stocking department and high in the plant department. The main thing to worry about is the nitrogen, which will be taken care if the lowtech set up is done well. Other salts that accumulate would likely do very little to the salinity, at least not to a level that would be lethal. I would be more concerned for the increase in minerals caused by evaporation and top offs, unless you are are using pure RO water. I bet you break down and do a waterchange out of boredom LONG before your fish kill themselves with there own salt.

If plants removed all dissolved solids in the water, if that is what youre asking, soft water species lovers would have much fatter pockets, nobody would be doing water changes, and I would be drinking the water out of my fish tank.
 

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I think you need to aim at 'minimal input' rather than 'maximum removal'.
After all, if something is never added, you do not need to worry about removing it.

Start with the least possible undesirable materials in the set up. Minimize toxic minerals to begin with. Good substrate, quality water, clean decor, rocks that do not add minerals to the water...
Note that many of the minerals plants need are required in very small amounts, and toxic in larger amounts. You want to start with a very low level of these so the plants are not deficient, but so there is room to add more as the plants grow without worrying that the level is getting too high.

Top off with RO.
Use a high quality fish food and count on fish food to supply most of the plant nutrients. Do not over feed the livestock.
If any livestock need to be medicated use a hospital tank.
Add only the bare minimum of fertilizer to meet any remaining needs of the plants.
Grow a variety of plants. Plants can take in minerals they do not need, and can take in minerals they do need in quantities greater than they actually need.
I do not know if some plants selectively take in certain 'undesirable' minerals in greater or lesser quantity than other plants.
I do know that some land plants are more tolerant of higher levels of 'undesirable' minerals. For example, Bermuda grass tolerates more boron than many other garden plants. They all need tiny amounts of boron, but where a well is high in boron, better grow Bermuda grass instead of Blue grass or Fescue. While I am sure the same is true of aquatics I cannot name species. I suspect that plants from hard water will be more tolerant of most salts and minerals in general. Would they actually take in such minerals? Thus remove them from the water? Or are they 'tolerant' because they have some method to exclude excess of toxic levels of these materials from entering their cells? (Thus leaving the mineral in the water- not what you are looking for here)
Plants from very soft water that can only be kept in such water are probably a poor choice for your set up. They probably have poor coping ability when there are too many minerals in the water, which is why they can only be kept in tanks with very low TDS. This is a short list of plants.
This last does not exclude plants from soft water in nature that do fine at many levels of TDS in aquariums. These plants (many, many of our aquarium plants) are quite adaptable, and are highly likely quite good candidates for your system.
 

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this is probably just a rephrasing of what everyone up above already said, but...

for the most part, a plant isn't going to remove and substance much more then that substance makes up it's tissues. If you are looking to remove salts, you will likely have to add a lot of other nutrients, and have some really quick growing plants. frequent water changes will probably be more effective, and require lower effort.

There are plants that can concentrate salts in sacrificial leaves/etc., but most of the ones I've heard of are terrestrial plants adapted for arid/desert conditions, and probably wouldn't work to well in an aquarium ;)

Anyways, back to rising salinity/TDS issues, I'd expect evaporation of hard water, or rocks/substrates to be more of an issue then feeding. when you do water changes, do you usually have to add noticeably more water then you take out? do you have any non-wood hardscape? what sort of substrate are you using?
 

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...a plant isn't going to remove any substance much more than that substance makes up it's tissues.
Actually they can. Plants can take in a lot more of many minerals than they actually need to live. They can act to purify the water in that way.
Per Diana Walstad, Ecology of the Planted Aquarium, chapter II.
Too long to quote here. Get the book and incorporate the ideas into the aquarium you are planning.
 

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Discussion Starter · #12 ·
Reading Walstad's book is what led me to come up with questions such as these!... I don't think Walstad's prescribed methodologies are the only way to do that however, and presume there must be a number of possible successful derivations of that as well, which is what I'm trying to explore in some part.

I just don't know quite enough about chemistry to sort some of these questions out, unfortunately.

I'm about to redo my current tank and substrate, which is why I'm asking these questions. It will be MTS over relatively fine silica sand. And I will be using RODI water for top-offs, so no worries there.

I suppose if 'normal' salt is the end-product of these biochemical processes, then there aren't going to be any plants removing that from the water however.
 

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Diana> thanks, I completely overlooked that aspect...

But I'd second the advice for picking up Walstad's book, I think it's an excellent resource, and covers a lot of aspects of planted tanks very well. There are many different ways to do a planted tank, and her book covers the low-tech dirted method pretty well, but a lot of the info can also be applied to other problems/setups, etc.
 

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In that case, it is more about balance than choosing the right species.

Most plants will remove from the water many things, so a mix of plants and a minimum of livestock will do what you want.

...'normal' salt is the end-product of these biochemical processes...
A circle has no end.
There is not an accumulation of sodium chloride in a fresh water tank.

Each molecule produced by one organism is used by another for some purpose, or simply sequestered, as plants can remove excess heavy minerals above and beyond their needs.

Here is what normally happens in a tank with too-few water changes:

Fish poop, fallen food, dead plant leaves, dead microorganisms all contribute their cells to the system.
Live macroorganisms (such as snails and worms) and microorganisms (Including fungi and bacteria) decompose these dead materials and break them down into their component molecules, usually adding more oxygen and sometimes taking some minerals out of the water as they decompose things.
The resulting molecules include ammonia and many other molecules that plants use as fertilizer. More microorganisms can also use the ammonia and other things. Specifically the nitrifying bacteria will remove the ammonia and add oxygen to it to turn it into nitrite then nitrate. These bacteria use some of the minerals in the water, and some carbonates. They do not get carbon from the dead matter; that has already been used by the first microorganisms to attack the dead matter.
Another side effect of all this is that the water becomes slightly acidic.

Net result:
1) Carbonates go down, allowing 'something else' to dictate the pH.
2) Decomposition tends to create acidic materials.
Therefore, the pH in the aquarium goes down.

In reduced pH, and especially if the carbonates are gone the nitrifying bacteria do not live very well, so they are removing less and less ammonia.
In a planted tank that specific problem is often masked by the plants removing the ammonia as a source of nitrogen.

Here is another side effect of too-few water changes:
Anything you add to the tank has minerals in it. Fish food, tap water, fertilizers, water conditioners, "aquarium salt"... read the label.
Without a way to remove them they all stay in the tank.
When water evaporates the minerals are left behind. This is very noticeable when the top off water is high in minerals, or if you are over fertilizing the tank. Excess fish food often becomes excess snails or fish (especially with live bearers).
I am not saying there is zero NaCl in this cycle, just that there are a lot more of other minerals and they are the ones you notice. "Aquarium Salt" is the only source of NaCl in enough quantity to accumulate like this. I sure hope you are not falling for the sales gimmick and adding salt to a fresh water aquarium! There are tiny traces of sodium in fish food, more than enough for that needs of a fresh water aquarium.

The best way to control this build up is to not add to it in the first place. Least minerals added means a slower build up.
Then balance the additions with removals.
The best way to export these minerals is by removing plants (trimming), remove snails and fish as they reproduce. Fast growing things (Plants and animals) incorporate into their bodies many of the minerals that you have added as fish food etc. When you prune, cull or otherwise remove the parts with those minerals you are removing those minerals from the tank.

So:
Set up a tank along whatever lines you want to call it. I do not care about the name.
You want a balance of plants and animals that will cycle through whatever you add to the tank so the plants and animals are thriving.

Use a good quality substrate. High CEC. This will trap a lot of minerals that the plants need, so they have a steady supply of what they need. This means the plants will grow strongly.
Have some faster growing plants. These will use up the excess minerals and you can export those minerals every time you prune.
Have good light so the plants have the energy to grow well.
Supply plant food as fish food, minerals that are deep under the substrate, and water column fertilizers. Be careful adding these to be sure they are added in something close to what the plants use.
Think of the fish as 'Fish Food Primary Decomposers'. They are the first in the line of organisms that are turning fish food into plant fertilizers. Only stock the fish you need to do that job. Do not overstock. Think of algae eating fish as 'Algae Recyclers'. Their job is to remove enough algae that the tank looks presentable, and turn algae into food for single celled organisms that will in turn make plant fertilizer out of it.

Think about each and every element that plants and animals need to live.
Provide each element in the best form for each organism.
Do not provide extreme excess of any of these.
Do water changes as part of the removal strategy.
 
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