Water Changes With Normal Parameters

[Spider Pig]

Do you need to do regular water changes if nitrate, nitrite and ammonia are all 0?

Have had tank set up for 6 months now and after 3 months have only done 15-20% water change every 4 weeks as the water parameters are all stable. Checked weekly at first then monthly as didn't change (before water change.) The tank is planted so I surmise that the nitrates are being used there. My understanding was that the main reason for water changes was to drop nitrate levels- if this is not a problem, then is there any reason to continue doing them, and if so why?

Have asked the same question on other forum, and although people stringently advise water changes for the benefit of the fish, no-one has come up for a good explanation of why this might be so.

 

[fishboy2]

yeah, u need to change the water once every 3-4 weeks to remove fish waste from the gravel to ENSURE your fish stay healthy. Plus ammonia and nitrite and nitrate can grow incredibly fast, so just keep doing wat u do now.

 

[Spider Pig]

Have been monitoring nitrate, nitrite and ammonia concentrations for the last 4 months and no spikes/ change. No significant change to fauna in last 3 months. With regard to hoovering gravel, I would normally have a good root around the substrate, but after reading this will only pick up surface stuff now: http/www.skepticalaquarist.com/docs/biofilm/devbio.shtml.

The question again is- if you test your water and the parameters are normal, then why do a water change? Obviously if they are raised then I'd change whatever is required to drop them back down.

 

[Bignose]

Firstly, if you are getting no nitrates, then the plants are probably doing all of the cycling for you. Aquatic plants generally prefer to take up ammonia as their nitrogen source (and a lot of them convert nitrate back to ammonia before use), so if the plants are taking all the ammonia, then there isn't any for the filter bacteria. So, to keep that tank healthy, your primary goal now is to keep the plants healthy. Lots of light, fertilizers if they need it, etc.

But, there are reasons to still do water changes. Firstly, and I think largely, you just want to refresh the tank. This is just like being able to open your windows for the first time after a long, cold winter. You want fresh air in the house, your fish want fresh water. Don't your fish always seem more perky after a water change? I've always noticed that mine do. And sometimes more frisky, too. If the water I use is slightly cooler than the tank water, it will sometimes trigger a spawning episode for my cory catfish. I've never seen them spawn unless it was after a water change.

Secondly, there are all manner of chemicals that get into the water. I'm talking carpet fumes, oils in the air from cooking, cleaners, cigarette smoke (if you smoke), fumes from candles or air fresheners, etc. etc. Again, for us, we just need to open the window or run an exhaust fan over the stove to refresh our environment. The amounts of these things in the tank are small, parts per million, parts per billion, maybe even parts per trillion. But, low level long-term exposure to chemicals can be just as bad as acute exposure to high levels. Water changes dilute these out and removes them.

Finally, it isn't as big of a deal without the ammonia-oxidizing and nitrite-oxidizing bacterial colony working, but your water still needs buffering capabilities. There are other bacteria in there releasing other acidic byproducts. Comparably, the rates of their excreting is probably 100 times less than the cycling bacteria, but they are still in there working away. If you never did a water change, you would still get a pH crash -- it would just take longer. Doing water changes replenishes the buffering capabilities of the water.

Still plenty of reasons to do water changes, though I would say that it is safe to either smaller volume or less frequent. I would personally still do as frequent but smaller volume water changes. I.e. 5% every week instead of 25%. Like I said, it just refreshes the tank like opening a window in a stuffy room.

 

[fishboy2]

I think another reason for a water change is to give the fish something to do, i mean in the wild they sometimes experience chemical and tempurature changes in the water, so i think its just to enforce there natural insincts.

 

[Spider Pig]

Interesting idea about the removal of volatile chemicals from the air. Have a carbon filter in place which should deal with a lot of that, but may remove it. Certainly the buffering idea is important. Live in a soft water area and have noticed pH swings over the day from the start of set up- may be that it is becoming saturated too quickly. As regards the breath of fresh air- seems intuitively correct, but my question is why this is so. Subjectively haven't noticed a big difference in behaviour before water change and after. I know that a drop in water temperature can trigger spawning because it simulates the monsoon or something, but it would be interesting to see if it has the same effect if new water is put in at exactly the same temperature as the tank water.

 

[Bignose]

Live in a soft water area and have noticed pH swings over the day from the start of set up- may be that it is becoming saturated too quickly.

This is kind of a confusing statement. What are you talking about that is "becoming saturated too quickly"?

As regards the breath of fresh air- seems intuitively correct, but my question is why this is so.

Well, at least part of it is because while ammonia is the primary waste of fish -- both from respiration and urination, it is not the only waste product. There are other chemicals that they release that other bacteria do come along and consume, and then those bacteria excrete waste as well. They don't get the same attention as ammonia, nitrite and nitrate, because those are the usual culprits of problems, but if you never do a water change, these other waste products will build up too. It is really as simple as that.

edited for spelling

 

[rdd1952]

Also, water evaporates between water changes so the level of undesirable things in the water rises in proportion as only the water leaves the tank. If you simply top off rather than doing a water change, you are allowing those items to build up.

 

[Tolak]

If you check the total dissolved solids I'm sure you will see an increase here. TDS measures anything dissolved in the water, organic, mineral, and often chemical.

 

[Spider Pig]

By saturated too quickly I was referring to the buffering capacity of the water. My understanding (which is long time from A-level chemistry) is that soft water has lower buffering capacity to hard water due to it's lower Ca ionic content. If the carbonate is saturated with H+ then the pH becomes more volatile as the buffering capacity is lost. Admittedly I have not checked the KH and GH for the tank and this is purely hypothesised from what I know of the tank

With regards to the bacterial waste, is that waste not used up by plants or disperse into the atmosphere? What happens to this waste in the external environment if there is nothing else to break it down if it is not used by plants or animals. What is the nature of this waste: toxins, minerals? This was the main reason I asked this question on the scientific forum. I don't question the validity of water changes, just the reasoning behind them.

With regards to water lost by evaporation, if the reason to do a water change is to prevent a concentration of waste, then replacement of the evaporated water with distilled water should be sufficient to dilute this without adding to the waste/ undesirables.

Is a high level of TDS dangerous/ problematic to fish? Does it have any benefits in providing nutrients for plants?

One question ultimately from this is whether it is possible to have a completely sealed ecosystem if adequately balanced in terms of flora and fauna.

Also how do you know how much water to change if nitrate isn't a problem and how do you work this out/ what factors do you base it on?

 

[Miss Wiggle]

Interesting, we've had a heavily planted tank that was basically looking after itself, monitored the major levels (pH, ammonia, nitrite, nitrate) and all was stable and good with them, did a fairly decent sized water change every couple of months, as you say just to refresh stuff. we never gravel vac (in heavily planted tank's and without any bottom dwellers it is often advised not too) so no need to remove water like that. Just topped off for evaporation mostly. Never had any problems, until this weekend when we pruned the tank too heavily and have started a mini cycle. However that's not relevant to the topic.

while it's not based on science but personal experience, i'd say if you have the tank set up correctly you don't need to do water changes as often as in a conventional set up, but just do them every so often and things should run smoothly

 

[Spider Pig]

Iwhile it's not based on science but personal experience, i'd say if you have the tank set up correctly you don't need to do water changes as often as in a conventional set up, but just do them every so often and things should run smoothly

That's the main question I'm asking- we all do these things but is there any good reason behind it. Is your's a purely planted tank or does it have fish as well? My set up is moderately planted but stable for the last few months- main reason do monthly water changes is to use the water to clean out the filter foam. Otherwise would be tempted to leave longer if all well.

 

[Miss Wiggle]

fish in but lightly stocked and heavily planted

yes there is reason behind it, as the others said above you can get build up of chemicals which needs reduction and water changes can trigger spawning in same fish.

 

[geo7x]

I think we ought to be careful about confusing no water changes with no filter.

This isn't really a matter of ammonia, nitrite and nitrate, as yes plants can reduce (or eliminate) all three, and it is perfectly possible to have a lowly stocked, highly planted tank with no filter but a powerhead for water circulation.

But water changes would still need to be done due to various toxins (like Bignose mentioned), dissolved solids in the water (again, like mentioned), to replenish minerals, and I'm sure that by doing water changes we are also preventing our tanks from becoming ridden with harmful bacteria and parasites that would otherwise be flushed out and diluted by the flow of the rivers in the wild (which a weekly water change would sufficiently recreate).

So I personally think that we should perhaps stop focusing on ammonia, nitrites, nitrates and the filter, because if the tank is so highly planted ammonia nitrite and nitrate will all be taken care of by the plants, and thus the filter is useless apart from it's water-circulating abilities.

 

[Bignose]

By saturated too quickly I was referring to the buffering capacity of the water. My understanding (which is long time from A-level chemistry) is that soft water has lower buffering capacity to hard water due to it's lower Ca ionic content. If the carbonate is saturated with H+ then the pH becomes more volatile as the buffering capacity is lost. Admittedly I have not checked the KH and GH for the tank and this is purely hypothesised from what I know of the tank

With regards to the bacterial waste, is that waste not used up by plants or disperse into the atmosphere? What happens to this waste in the external environment if there is nothing else to break it down if it is not used by plants or animals. What is the nature of this waste: toxins, minerals? This was the main reason I asked this question on the scientific forum. I don't question the validity of water changes, just the reasoning behind them.

With regards to water lost by evaporation, if the reason to do a water change is to prevent a concentration of waste, then replacement of the evaporated water with distilled water should be sufficient to dilute this without adding to the waste/ undesirables.

Is a high level of TDS dangerous/ problematic to fish? Does it have any benefits in providing nutrients for plants?

One question ultimately from this is whether it is possible to have a completely sealed ecosystem if adequately balanced in terms of flora and fauna.

Also how do you know how much water to change if nitrate isn't a problem and how do you work this out/ what factors do you base it on?

Well, you're understanding is a little off. The word "saturation" there is completely wrong. Saturation involves adsorption or absorption, or some sort of "filling up" of an object. Some examples of the correct use would be when water has absorbed all the oxygen it can, it is right to call it saturated. When carbon has has all is adsorption sites filled, then it is called saturated.

The word you are looking for would be consumption. When all the buffering agents are consumed, then the pH starts dropping. Each H+ generated primarily as the end result of the cycling bacteria would react with a buffering agent. Once all the buffering agent is used up, then the excreted H+ cause the pH to drop. The best analogy is like a tank of gasoline. The car can use gasoline to keep going at the same speed, but once the gas tank is empty, the car slows down pretty quickly, just like the pH can drop pretty quickly.

Your word choice there is what confused me.

I have no doubt that some of the waste is used by plants, but I also have no doubt that it isn't all of it. I am sure some of the waste has to get washed away eventually and then is taken care of by something far, far away from the local environment. There are no perfectly closed systems in nature, unless you consider the entire Earth itself. So, while you can get close in a home fishtank, I think that trying to achieve perfectly closed is a fool's errand.

Having a high level of TDS can be bad for a fish -- it primarily depends on the species of fish. Plants in general do not like high TDS either, there is a nice middle zone between too hard and too soft for most plants. Most plants do better in slightly alkaline waters than acidic, though again, it is best not to stray too far from the plant's ideal zone. This will again depend heavily on species.

The nature of the fish waste is going to be complicated. Firstly, the big dogs. Ammonia is going to be around 90% of the waste, from both respiration and excretion. Urea is going to be close to the rest of the 10%. But, then there are all sorts of other things that fish excrete in small amounts -- phosphorus compounds, other nitrogenous compounds, etc. Look at Naylor, Moccia, and Durant "The Chemical Composition of Settleable Solid Fish Waste (Manure) from Commercial Rainbow Trout Farms in Ontario, Canada" in North American Journal of Aquaculture 1999. Here's a quote from the abstract: "The manure samples from the commercial farms averaged 2.83% nitrogen (N), 2.54% phosphorus (P), 0.10% potassium (K), 6.99% calcium (Ca), and 0.53% magnesium (Mg) on a dry-weight basis. The concentrations of the metals, arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), iron (Fe), mercury (Hg), manganese (Mn), nickel (Ni), lead (Pb), selenium (Se), and zinc (Zn) were also measured. Mean concentrations of these metals ranged from 0.05 mg/kg for Hg to 1,942 mg/kg for Fe."

Lots and lots of stuff in there. There are all sorts of different processes to handle these. One of the easier ones would be for the plants to taken them up as their required micronutrients and then the fish eats the plant. But, most processes are not that simple. Most probably involve some sort of microorganism, and them some kind of worm or shrimp or something like that, which then involve maybe even some outside terrestrial animal, who really knows? This is why I say that there are no truly closed environments in earth, and trying to have one in 50 or 100 or 1000 gallons in your home is probably a fool's errand.