automatic water change, via plants

[Magnum Man]

so, my tanks have most all been running for several years now... they are all display tanks, and as such, are all over crowded... over filtered, and have been working out, most are open topped, thus have a pretty high rate of evaporation... they have been running long enough, that I know my terrestrial plants growing out of my tanks, are pulling about 5 gallons on average of water out of each tank, per week... I count the plant drawn water as part of my water changes... I understand that you can't count evaporation as water change water, as that concentrates impurities... but with the volume of water being removed by my plants, I'm only vacuuming the substrate to remove an additional 5 gallons from each tank every other week, I do it weekly, if I have time, but in reality, it's been every other week... I have a lot of vining plants growing out of my tanks, this requires topping off of the tanks, about 3 times a week, of 3-5 gallons of RO.... I have several very sensitive fish, and if my stocking levels were more normal, the plants could almost replace the water changes slupping of buckets... I do have tanks that I vacuum right to the toilet... I refill RO water that is pumped to the tanks, from an RO collection tank...

I would bet, if the plant draw was big enough, and the stocking level low enough, that one could get to the point, that a weekly / monthly substrate vacuum would be all that would be needed, and even at some point a pump, to a drain line could be incorporated, eliminating the buckets completely ( thinking ahead, before I get to old to be slupping buckets at all )

of course this is dependent of the plants doing their job, and maintaining an effective amount of water draw, as they age... but it's amazing how much water 30 feet of Pothos vine will draw... I'm not saying that you wouldn't need to do water changes, as I feel it's important to vacuum the substrate, but I'm comfortable counting the water drawn from the tank, as part of the water change volume needed...

 

[FranciscoB]

That sounds very interesting. Plants are great. However, how do you estimate how much water is lost to evaporation, and how much is “water taken by the plants”?

 

[MaloK]

Also a thing to consider:

Plants take only what they need and leave the rest there. So basically they would never be able to replace water changes.

And are not going to have any effects on some byproducts that are still going to build up.

But still, an "auto-top-off" working with gravity could be installed on each tank and save you a part of the job.

The most difficult part would be to add overflows on already running tank without serious intervention. And be able to completely automate water changing.

With a good heater in the holding tank... This way you could do "Phantom" water changes of any size at any time.

 

[Magnum Man]

pretty easy to estimate, when you 1st add the plants, and they are drawing next to no water, and then months later, when you are replacing 3-4 times more water, than you were for evaporation alone... or if you incorporate the vines into a covered tank ( most of mine are open top ) but several have pretty tight lids to either control the room humidity, or contain the fish...

35 years ago we lived in a house with a huge main room, with a lot of glass, on the east and south sides... I discovered this by accident back then, we had a lot of houseplants in that room, and a few aquariums... one vine put down a root into a tank, and when we moved from there a couple years later, we had 50-60 feet of vine growing to those windows, out of that aquarium

 

[Magnum Man]

@MaloK thats a good starting point for discussion...
do we think they draw the nutrients out of the water, or just draw the water containing the nutrients??? there would be a difference there...

mine precipitate, the leaves actually drip water... I'm curious if that is extra water, more than the plant needs, to get the nutrients it needs, out of the tank water, or if that is plant "urea" so to speak, the plant is dripping out extra nutrients more than it needed in the water it's drawing in from the tank???

 

[GaryE]

I always look at these things and feel blind. If I were a chemist and had a lab, I could monitor what was going on. But I'm not and I don't.

I moved from a house that usually had a tds of 70 to 85 from the tap. Now I'm 9 hours east of there, with a tds of 60 to 85 from the tap. But my hobbyist way of measuring minerals gives me a number, but doesn't tell me the components of the water.

The breeding patterns, sex ratios and plant growing possibilities are different here. Fish species that were easy to breed there are harder here, and vice versa. I have a number that's more or less the same for both places, but I don't know what makes it up compared to what made it up in Montreal.

That's my problem with trusting my plants as filters. What do they remove, and what do they leave behind? They are clearly helping for my water quality. I have all healthy plants of all sorts popping out of filters and growing via roots in, plants out all over the fishroom. I've had 30 foot vines. I had a fishroom 18 feet long with a Pothos vine looped the full length of the room four times before I moved. It drew from three or four tanks it had rooted into. I share your love of terrestrial plants with aquariums.

But I still do full water changes of 30% because while I know the nitrogen cycle is under control via plants, the nitrogen cycle is just one process among many. We can test it, so we get its importance. There are so many things we can't test - so many minerals, hormones, etc that I trust no system but regular changes.

I stock lightly, because I like to. To me, @Magnum Man , your tanks are brutally overstocked. But the fish seem to be doing well, and the plant filtration and your maintenance regime are working. My lighter stocking plant root tanks are also doing well. So we're onto something. Because the plants feed and extract their food, I'm concerned about the non food elements I can't measure. Our archaea and bacteria colonies also feed on ammonia and ammonium, but leave many problems behind untouched. Just having a cycled tank doesn't take away the need for water changes. So where do we stand with plant root tanks? I don't know, so I would rather err on the side of caution.

 

[Magnum Man]

that's kind of the point of the post before this one... are the plants just drawing the nutrients they need out of the water, and leaving the rest in the tank??? or are as I suggested, possibly drawing in a volume of water with no regard to what's in it, using what they need out of that water and precipitating the contents of the water they can't use...

my plants definitely precipitate... it would be interesting to know the contents of that precipitate...

 

[GaryE]

Yeah, but how can we know with the resources we have? That's where it breaks down in my view. I know they pull water up, but since they're feeding, they won't take everything in.

I wish I knew more about the process, in detail. But what you have in your water is probably different from mine.

 

[Naughts]

pretty easy to estimate, when you 1st add the plants, and they are drawing next to no water, and then months later, when you are replacing 3-4 times more water

IMO this reasoning is flawed. Plant growth rates vary depending on season, light levels and temperature, so their water uptake will be inconsistent. The evaporation will additionally vary with temperature and surrounding humidity levels.

 

[Wills]

I have a combination of floating plants, heavy tank planting and terrestrial plants growing from the surface of most of my tanks and it allows me to maintain low to 0 nitrate but I still do regular (in all honesty not weekly) water changes because there are other things that cannot be dealt with through these processes.

The biggest ones are hormones from the fish, the various elements that they emit to do with breeding, growth, dominance really builds up and will effect them and their tank mates. I suppose in nature the natural flow of water (how ever sporadic) will flush these through.

One big game changer I realised was the effect that aquarium plants that break the surface make! Especially if they flower, they seem to be the difference between my nitrates sitting at 0 or 10-15.

Wills

 

[connorlindeman]

Whenever this question comes up I always just wonder what the big deal is with giving the fish some fresh water. In their natural environment they don't have to live in the same 50 gallons of water day after day.

 

[Uberhoust]

Interesting idea but I believe you will be left with water that has a high concentration of some waste products, with the other waste products being handled by the plants, overtime the unabsorbed waste products may start to cause issues, a fish tank is pretty close to a closed system already it would be more so with your suggestion. As @GaryE mentions this would be difficult to assess without some laboratory equipment. Why not keep with the plants but automate the filling of the tank. There are any number of flow control systems to fill a tank to a specific level then stop, both electrical with water level sensors but also mechanical with toilet like float controls. If you have RO water that you generate you could pipe that to your tank using an RV water pump that shuts off when the water pressure exceeds a certain limit, ie when the float valve closes. You would also need an automated overflow system which could be as "simple" as an overflow drilled into the tank that drains into the yard or sewer system. In regard to the buckets, why not just just run your python or other siphon directly into your sewer or out the window into the yard, then you would not have to transport the full buckets around the house. Just some thoughts.

 

[Magnum Man]

I appreciate the honest conversation... "if the plants take in water, with any and all impurities, that is equal to a water change... I don't know, but find it very likely to be the case, rather than separating out just the nutrients that they need, causing them to concentrate in the remaining tank water... I'm wondering what it would take to collect and anylize that precipitate...

I seem to remember dying water for plants to suck up, as an expiriment back in school...

as far as automating the systems, I feel that would take me too far out of touch with the condition of the aquarium..

 

[WhistlingBadger]

Personally I think you’re probably onto something. It seems to me that plants suck up water and whatever happens to be dissolved in it, as shown in that dye “experiment “ some of us did when we were kids. Terrestrial plants even take up herbicides through their roots, so obviously they aren’t picking and choosing.

On the cellular level it gets more selective I’m sure. What happens to the chemicals a plant can’t use? If the hormones and such are excreted through the roots, that would mean some potentially harmful substances are being dumped back into the fish water. If they are digested and metabolized by the plant, which seems likely to me, then it’s doing the same thing as a water change.

But how to know for sure? No idea. You pay your money and you take your chances. If it were me I’d keep doing water changes anyway. But it is a really interesting idea.