Advice sought on "Over-filtration"

[Darkmaverick]

Hi all,

I would like some advice regarding 'over-filtration'. Generally, im a very detailed and thorough axolotl guardian and try to provide them with the best. I have an external canister filter suited for my 4 foot by 2 foot by 2 foot tank and have set the flow rate as low (to avoid high water flow stress). However, i am concerned that i may be over-filtrating their tank and thus would like to find out the following:

- Over filtration occurs when the water quality almost becomes like 'distilled' water clean. Meaning it has lost of a lot salts and thus affect the hardness of water and can be detrimental to axolotl health. How do i firstly detect if my tank water is overfiltered? Do i do so by testing for hardness?

- What are some of the clinical signs demonstrated by axolotls living in 'over-filtered' water? Would aquatic plants be affected and how so? Do they turn brown and die for eg?

- If over-filtration is indeed occuring, what are the steps to rectify it? Some sites recommend adding salts to the water to boost hardness. However, i am most paranoid about using chemicals and salts as they require accuracy and precision. Do i simply take it off the filter system or try downsizing a filter?

Thanks and regards

 

[geosheets]

I don't think it's possible to 'over filter' your tank. Your filter should not change the water chemistry at all assuming it's a filter designed for aquaria use. Excessive current/flow would be the greater concern as far as axolotl's go.

I think what you may be referring to is when one uses a reverse osmosis system (softened and distilled water also) that most impurities are removed from the source water. If you are using RO, softened, or distilled water you will find the ph and hardness is very low. In this case you will need to add buffers to bring these back in line. There are several additives on the market designed just for RO water if this is what you are using.

 

[Darkmaverick]

Yes, i was initially surprised and confused that there is such a thing as over filtration. However i was reading up axolotl.org under the heading "housing" which mentioned the following:

"However there is evidence of the phenomenon I will call "over-filtration", and this can be stressful to axolotls. By over-filtration, I mean too high a turnover and/or too much biological filtration. I will discuss this further on. This is more frequently encountered in the use of external filters, because they are intended only for large aquaria, yet novice keepers may utilise them with smaller accommodation. Over-filtration leads to water that is, aside from dissolved salts, like spring water - a rather hostile environment for axolotls."

I was concerned at this point as i had no prior knowledge that this can occur!

 

[Kal El]

G'day,

I think you may have misread the information posted on the site. It says:

"Over-filtration leads to water that is, aside from dissolved salts, like spring water - a rather hostile environment for axolotls."

To me, this simply means that the filter turn over it too great which, in turn, doesn't give nitrifying bacteria the "chance" to colonise the filter media. But this doesn't take into account that bacteria will also settle on ornaments, glass, and so forth. Spring water is some what analogous to distilled water in that it will not have dissolved electrolytes, and it definitely will not have bacteria. The statement above says, "aside from dissolved salts".

In essence, the only way of permanently softening water is to export ions such as Ca and Mg, by using ion-exchange resins, peat, R/O (reduces the buffering capacity of water), and even snail shells.

Jay.

 

[Kaysie]

Spring water differs from distilled water in that it DOES have dissolved salts (or electrolytes, if you may).

Over-filtering your water is having too big of a filter for your tank (as opposed to too small). You grow lots of bacteria, which can strip the water of 'good stuff' (minerals, nutrients other than ammonia and nitrites), which are taken up by the bacteria. But a bigger issue with having too big of a filter is more a matter of having too much flow. Overall, it's not an issue unless you're using a filter rated for a 55 gallon tank on 10 gallons of water.

 

[Darkmaverick]

I appreciate all the replies to my query but i am still rather confused. Perhaps i should rephrase my question to clarify. Firstly i would like to ensure that my current understanding of the definition of 'over-filtration' is correct.

In this case, over-filtration refers to 'sub-optimal' nitrifying bacteria colonisation attributed to excessive filtration turnover, rather than softening the water by removal of dissolved salts. Therefore my initial interpretation by testing for water hardness is irrelevant. I definitely do not use R/O, distilled or softened water for my tank. And im absolutely glad i got this clarified because it doesn't make sense that the filter would soften the water.

However, in this case, again it doesnt add up because as you mentioned, bacteria colonisation can occur on any surface in the tank, including the glass, plants and even substrate. The filter media for bacteria colonisation itself although plays a part, is not exactly be all end all.

Furthermore, nitrifying bacteria aids in the breakdown of nitrites to nitrates which would be utilised by the plants as a food source. In the event that there is 'sub-optimal' colonisation of nitrifying bacteria, i would theoretically expect the nitrite level to be higher and nitrate levels to be low. This could result in nitrite toxicity in axolotls and poor aquatic plant growth because of low utilisable nitrogen source. Both nitrite and nitrate levels are easily measured and would not have the opportunity to creep up that drastically with regular water changes. Bacteria would still be able to colonise over time although less efficiently.

Im just really puzzled why the site refers to 'over-filtered water' as hostile 'spring water with dissolved salts', because if dissolved salts are present (and therefore hardness), does the hostile environment come from low/absent bacteria count (as in sterile ionised water)? Maybe im just pedantic.

 

[michael]

In Frank Indiviglios new book "The Everything Aquarium Book" he talks about a wet dry or biological system working to well. On page 28 Frank says "Nitrifying bacteria can grow so well in a well-managed wet/dry system that their nitrate production can actually be detrimental to the aquariums inhabitants. Maybe this has something to do with an overfiltered tank. I know too much oxygen in the water can also be a problem with some amphibians.

 

[geosheets]

I guess there are a couple extreme circumstances that could be considered an 'over-filtration' since the bacteria colony is going to grow and shrink depending on the amount of food(ammonia) it has available.

As Kaysie pointed out, the bacteria colony could become so large that it actually becomes a dominating organism within the tank and could deplete the water of nutrients. The tank would then require constant water changes to keep the nitrates anywhere near acceptable levels. I would think that the tank would have to be extremely overstocked to even reach this level of nitrifying bacteria.

The second scenario I can think of is if the tank had a very large area for bacterial growth but only minimal ammonia sources. In this instance the biofilm could become very thin and be very susceptible to to damage. The water would probably be very similar to spring water in this example.

 

[Kal El]

Spring water differs from distilled water in that it DOES have dissolved salts (or electrolytes, if you may).

Over-filtering your water is having too big of a filter for your tank (as opposed to too small). You grow lots of bacteria, which can strip the water of 'good stuff' (minerals, nutrients other than ammonia and nitrites), which are taken up by the bacteria. But a bigger issue with having too big of a filter is more a matter of having too much flow. Overall, it's not an issue unless you're using a filter rated for a 55 gallon tank on 10 gallons of water.

Now my definition of over-filtration has changed some what: Nitrifiers (a.k.a. nitrifying bacteria) are not the only bacteria that are present in the tank. There are other bacteria that are responsible for metabolising organic matter. This community of bacteria contribute greatly to the biological oxygen demand (BOD). If an excessive amount of organic matter is being metabolised (over-filtration) in the tank, this negates nitrifiers from doing their "job" (i.e. hinders nitrification) because oxygen will be scarce.

I would think that the tank would have to be extremely overstocked to even reach this level of nitrifying bacteria.

In this case, there would be a lot of waste being produced in the form of mainly ammonia, which will only add to the bioload. Most tanks that have an ammonia concentraion greater than 5ppm will always have the "nitrite spike", and the tank never completes the nitrification cycle, i.e. no detectable nitrate.

The second scenario I can think of is if the tank had a very large area for bacterial growth but only minimal ammonia sources. In this instance the biofilm could become very thin and be very susceptible to to damage. The water would probably be very similar to spring water in this example.

How so?

Furthermore, nitrifying bacteria aids in the breakdown of nitrites to nitrates which would be utilised by the plants as a food source. In the event that there is 'sub-optimal' colonisation of nitrifying bacteria, i would theoretically expect the nitrite level to be higher and nitrate levels to be low. This could result in nitrite toxicity in axolotls and poor aquatic plant growth because of low utilisable nitrogen source. Both nitrite and nitrate levels are easily measured and would not have the opportunity to creep up that drastically with regular water changes. Bacteria would still be able to colonise over time although less efficiently.

I don't really know what you're talking about here. Plants can still thrive in a tank that doesn't have or has a very minimal concentration of nitrate. In actual fact, plants favour ammonia and nitrite over nitrate. Plants can compete with nitrifying bacteria, which is why some people are reluctant to have a heavily plant-populated tank.

When I said that bacteria will colonise ornaments, etc., I was referring to the fact that bacteria seldom remain in water. Bacteria are drawn to such surfaces due to Brownian motion, which is characterised by the random buffeting of molecules. When bacteria come close to such surfaces, weak forces such as van der Waals forces and electrostatic forces take place, and bacteria become irreversibly adsorbed to the surfaces. This is the beginning of biofilm formation.

Jay.

 

[Darkmaverick]

Im glad this thread has generated interest and academic discussion. This is how education is perpetuated.

I think the pivotal eureka moment were the posts by Kaysie and Michael who defined 'over-filtration' as having excessive bacteria colonisation, as opposed to the initial interpretation of 'sub-optimal' bacterial colonisation because they dont have the chance to do so. This is part where i personally felt it became logical. Bacteria in this case refers to not only nitrifiers by other bacteria types.

Geosheets has also allayed my concerns of filtration leading to water softness with his informative posts.

Kal El has suggested that excessive bacteria population would interfere with nitrifiers to efficiently convert nitrites to nitrates due to reduced oxygen instead of stripping out useful nutrients and minerals. This is another interesting notion that is indeed food for thought.

Another new thing i learnt today was that aquatic plants prefer ammonia and nitrites over nitrates! I have always thought of aquatic plants using nitrates as a nitrogenous source. In this case, do aquatic plants therefore have a buffering capacity against ammonia and nitrites?? (Meaning the presence of aquatic plants will utilise ammonia and nitrites and thus lower their levels in the water)

As for biofilm formation, i wasn't confused about that. I understand how they form (glad i kept my year 2 lecture notess!!) but im thankful that the information is shared.

Cheers

 

[Kaysie]

Yes, plants will help prevent ammonia and nitrite spikes. Some people prefer heavily planted tanks over filters. Me? I can't keep plants alive to save me.

 

[Kal El]

Another new thing i learnt today was that aquatic plants prefer ammonia and nitrites over nitrates! I have always thought of aquatic plants using nitrates as a nitrogenous source. In this case, do aquatic plants therefore have a buffering capacity against ammonia and nitrites?? (Meaning the presence of aquatic plants will utilise ammonia and nitrites and thus lower their levels in the water)

Yes, plants will help prevent ammonia and nitrite spikes. Some people prefer heavily planted tanks over filters. Me? I can't keep plants alive to save me.

To be more specific, plants prefer ammonium over ammonia and nitrate.

Dark Maverick, I can appreciate why you'd think that plants utilise nitrate primarily, because this is what garden plants do. However, aquatic plants are different in this respect. Studies have shown that plants don't start taking up nitrate until all traces of ammonium have been depleted. The uptake of ammonium actually inhibits the uptake of nitrate. This phenomenon is not only observed in aquatic plants, but also by fungi and algae.

Jay.

 

[Kaysie]

Dark Maverick, I can appreciate why you'd think that plants utilise nitrate primarily, because this is what garden plants do.

Actually, most agricultural fertilizers are ammonium based.

 

[oceanblue]

Despite reading this thread three times I'm puzzled by what overfiltration is supposed to do to the water and what overfiltered water would look like on chemical analysis (presumably it is wonderfully clear optically!).

I think this term is a concept which has no sensible use in tank management: Use a filter which achieves appropriate water turnover without too disturbing a current and monitor the chemistry.

I understand there are species differences in ammonium, nitrite and nitrate preferences in both aquatic and land plants, but most aquatic plants prefer ammonium and if using nitrite or nitrate have to use energy to convert them back to ammonium before they can use the nitrogen for protein synthesis.

I run mainly very heavily planted tanks, some without filters. They usually test ammonia-trace, nitrite-nil, nitrate-nil. They are often murky and full of crud. I suppose this is why I haven't worried about overfiltration!

Nitrogen from added worms is probably mainly removed as watercress cuttings, but some may be metabolised by biofilms on the plant surfaces and by anaerobic breakdown in the mud layer. I do daily 1% water changes mainly because without them the water gets browner and browner.

 

[Kal El]

Actually, most agricultural fertilizers are ammonium based.

No doubt there.

However, most garden/agricultural plants prefer nitrogen in the form of nitrate. While some plants can take up ammonium; ammonium is readily converted to nitrate nitrogen by microbes in the soil.

Jay.