There Is Allot Of Argument

[Tolak]

I have a pair of 150 gallon tubs, indoors, right next to each other. I could easily bridge these, run a canister with one end in each tub, and effectively have 300 gallons. If I did no water changes I would have problems.

A large centralized system would have the same amount of gallons as a decent size pond. The largest I have seen personally had 300 forty gallon tanks, huge uv sterilizers, and a 300 gallon tub full of bio balls for bio filtration. Do the math, figure out the gallons running. Daily 20% water changes on this system, a large angel breeding setup. No water changes would be a problem.

Ask CFC, with a tank that I believe is 900 gallons, what would happen if he did no water changes.

 

[nickelplates]

^ Yes, but assuming that your pond is outside, there is a thing called rain, which will fill the pound up, and heat/sun, which will evaporate water, taking the hormone with it.

have to completely disagree there - evaporating water doesnt carry with it anything. take for example a bowl of salt water, when evaporated will leave behind salt. just as a bottle of "mineral water" when evaporated will leave behind all its minerals (usually a brown looking film on the surface you've evaporated from)

plus, where does rain come from? it's not new, its been used over and over again! bacteria will grow to ensure things stay balanced, and (presumably) in a larger tank, with no water changes, additional bacteria would eventually arrive to take care of things!

As you yourself say the water evaporates and leaves 'stuff' behind then falls as rain so the 'stuff' isn't in the rain (whether it is salt hormones or whatever). In fact apart from what it picks up from the air rain is distilled water.

 

[BigC]

Could quite easily be the case with proper stocking levels and proper filtration and I mean proper filtration with certain aspects of the media changed on a regular basis. And also with plants assimilating as they do in nature i.e. phyotosynthisis, CO2 and Oxygen levels But if it were me I would still like to replenish with some fresh water on a regular basis.
Regards
BigC

 

[Esfa]

although... if you have it densely planted and low-stocked then there should be no problem with nitrates, but i'd still do water changes for any chemicals etc...

 

[jarcher1390]

im not an expert but it does not matter what size tank you have probally it will not work as. in the natural habitat it rain we all know it rains and it perculates throungh the ground picking up mineral from wethered parents rock. Its not just H2O in your tapwater which is important there is minerals which our body need and the fish bodies to.
As for the hormones they will probally get brocken down naturally. given a big enought tank the rate of decomposition of the hormone will ballance out with the volume of water.
At work our biggest system is 3000 gallons and guess what we still have to do water changes if we did not many fish will die.
Jonny

 

[Proud Texan]

If im not wrong plants use nitrate for food so if its freshwater and planted i have no doubt it would not need water changes.

 

[Esfa]

If im not wrong plants use nitrate for food so if its freshwater and planted i have no doubt it would not need water changes.

it depends on the amount of plants, and what fish.

if the ank was full of plecs, puffers, and bichirs then there would be a lot of nitrates being produced and therefore too much for the plants

but if there were platys, guppies and swordtails then there would be no problem with nitrates.

still, it'd be nice for at least 35% water change a month.

 

[Tolak]

Nitrate is not the only end product of keeping fish in a closed environment. Total dissolved solids must be taken into account, as well as any air borne pollutants that may enter the closed system.

 

[geer head]

IMO, I don't know of a body of water with living fish that has the same water it had, let's say 10 years ago. Any natural water outside is subject to movement: evaporation, rain, flowing rivers, etc.

It's a real interesting idea. I think it could be possible to have a tank for a few years and not need to do water changes (only top up evaporated water). If you have a good CO2 and O2 cycle, proper filtration, enough plants and nutrients, by topping up the water every now and again it would be much like you would find in real life. The only problem imo that could still foul up this plan would be the buildup of minerals, etc in the water. In a real pond, everything can sift through the ground and 'effectively' remove itself from the pond. So I think you could easily have a tank that size and not do a water change for a year or two, but after that??

 

[nickelplates]

If im not wrong plants use nitrate for food so if its freshwater and planted i have no doubt it would not need water changes.

it depends on the amount of plants, and what fish.

if the ank was full of plecs, puffers, and bichirs then there would be a lot of nitrates being produced and therefore too much for the plants

but if there were platys, guppies and swordtails then there would be no problem with nitrates.

still, it'd be nice for at least 35% water change a month.

OK that makes sense, if we have enough plants we don't need to do water changes to remove nitrates, in theory you can also do the same with a filter that grows anearobic bacteria.

BUT

An aqaurium is a body of water whose volume gradually reduced as it evaporates, as has already been discussed only water is lost (and of course replaced by the aquarist topping up but we will assume that he uses distilled water). A huge variety of substances gets into the tank from the air, the aquarist's hands, the food we feed them, plant fertilizers and so on, some of this is food for plants and bacteria but everything else that dissolves accumulates in the water, this even includes traces of contaminats in the fertilizer. The only sensible way to dilute these materials is to remove (and replace) some water. The upshot of this is that in the end you will have to do a water change.

If you asked can we reduce the need for water changes by using strategies to remove nitrates the answer is yes, and it is probably easier to do so in a larger tank. The question is can we get rid of water changes altogether, the answer is an emphatic no, sooner or later the water will acquire levels of one substance or another that are dangerous to the fish and you will have to do a water change, when will this be? I don't know but it will happen.

 

[BigC]

Yeah. At a certain point in time, although not immediate, some sort of replenishment will be called for.
Regards
BigC

 

[jarcher1390]

its all to do with minerals dissolved in the water. take calcium for bones. when a fish grows it will take calcium out of the water and be put into the bone strycture. lets say you had 1 neon tetra in 3000 gallons there would be enought calcium in the water for it to grow for its full life however if you stuck and pacu in a 30 gallon tank it would quickly use up all the calcium and would not be be alble to grow and eventually die. if water is changed there is more calcium for the fish.
Jonny

 

[andywg]

It's an interesting point. Many SW enthusiasts prefer not to do water changes and keep reefs. Corals are far more sensitive to a number of pollutants than fish. The key is making sure you are taking care of things.

There was a debate similar to this in the science forum. Spider Pig referenced a paper showing that a Tilapia fish farm was doing fine on a closed system (over 400 days and the growth rates of the fish match those of the control).

So, in theory, yes, one can eliminate water changes, but in practice it is a lot of work and water changes are so cheap it just doesn't often end up worthwhile. The reason so much is spent on equipment like sumps and protein skimmers in SW is the added cost of salt makes water changes a lot more expensive.

Simple question, complex answer...

 

[backtotropical]

Good thread, Proud Texan, but i'm afraid that what you have heard is 99% wrong.

Have you ever heard of 'Old Tank Syndrome'? Have a read of the link below as it explains how it is entirely possible to have fish living in a tank which receives no water changes at all, but it certainly doesn't mean that they are healthy or happy. I suppose it depends on what you mean by 'need' a water change.

[URL="http/www.bestfish.com/oldtank.html"]http/www.bestfish.com/oldtank.html[/URL]

A self-contained eco-system, theoretically should be possible to achieve but in practice it is almost impossible, or certainly at least impractical, as Andywg says. Obviously the filter bacteria which we all know and love take care of the ammonia and nitrite. Plants can take care of nitrate but won't always do so as they prefer to feed on ammonia. Therefore, the tank would definitely need to be lightly stocked to avoid a high nitrate build up.

As previously mentioned there is then the dissolved mineral content ot Total Dissolved Solids (TDS) as it is commonly known. An ever increasing TDS is not good for fish and is difficult to remove without performing water changes.

Assuming you figure out a way to deal with that, then there are, as Tolak mentioned, household air-bourne pollutants which you maybe don't even consider as a threat to your water quality. The most common ones are probably dust, deoderant, air freshener, cigarette smoke etc etc. Given time these will build up in the water and will obviously cause distress to the fish at the very least.

There would also always be a constant battle against kH and pH crashes due to the acids which are the by-product of the nitrogen cycle taking place in the aquarium filter. This would need to be countered by slow release calcium carbonate (or similar) based decor or substrate or by some other means.

As you can see, its not quite as easy as just having 300 gallons +.

As the article i linked to above states, it is possible to keep fish in a tank which receives no water changes, and i hear of it all the time, usually with goldfish which are crammed into a 5 gallon bowl for 10 years (don't get me started), but it is through ignorance that people think this is ok, not education.

The self-contained eco-system you speak of is theoretically possible, but almost impossible to actually achieve. Anyone can keep fish in a tank with no water changes, almost nobody can create the perfect self maintaining tank.

Even if it could be done, it would be due to the filtration devices put in place (including live plants, activated carbon etc etc), very careful stocking ratios, careful regulation of the pH and hardness of the water and measures which would have to be taken to eradicate the possibility of contamination from the world outside the tank, and certainly nothing to do with the fact that the tank is over 300 gallons.

Hope this helps you.

Cheers

BTT

 

[iankent]

Even if it could be done, it would be due to the filtration devices put in place (including live plants, activated carbon etc etc), very careful stocking ratios, careful regulation of the pH and hardness of the water and measures which would have to be taken to eradicate the possibility of contamination from the world outside the tank, and certainly nothing to do with the fact that the tank is over 300 gallons.

well put BTT! next to impossible to do, but still potentially doable!