The maths of Water Changes

@Biggles, that is an interesting observation about the ammonia. I also read that plants prefer this and you would be quite right that it would make more sense to put them before the bio filter.

I read the book by Diana Walstead and she is of opinion that a heavily planted tank should not have a bio filter as it will be in competition with the plants.

Regarding your nitrate levels, maybe it would make sense to dial your flow rate a bit down to keep the nitrates up? Alternatively, get some more fish...:nuts:

 

@JJFury, the flow rate is on the high side. This is more of an insurance policy than anything else. My tank has to run un-attended for 5 weeks straight. The equivalent tank would have gone through 3 major water changes and 2 tank cleans during that period. Mine just ticks over. The tank gets cleaned every 7 weeks. I believe the fish are much better of for it. Remember the temp only has slight day night variations. Nitrates are steady (flat line) rather than a gradient. pH is constant. A water change system fish feels the water getting grottier and grottier, then all of a sardine the water changes and they get a temp, pH and clean water shock... as far as my fish are concerned they live in a constant environment.
The down side is I am using 100% more water than equivalent water changes because I dilute and then remove. Rather than remove and then add new water.

 

This is the reason why we do weekly or fortnightly water changes (most of us anyway). Yes your N2 level increases in a linear fashion which is determined by bio-load, natural consumption (plants and bio filtration) and the human hand. The curve shown earlier is for a tank with no interference from any of these 3 factors. So in other words high stock levels will increase the rate of saturation, as well as a heavy hand at feeding times. Bio filtration will remove NH3 and NO2 at rates determined by the quantity of bio culture available in your filter, which points to what was said about filter types and sizes. However this will also be affected by how efficient that said filter is maintained. Plants prefer N2 in its rawest form so it will consume faster degrading N2 components like NO3 first before tackling stuff like NH3 which is far more stable. It is true that fast growing plants will remove more quantities of NO3 due to the plants needs BUT these fast growers will also starve the micro nutrients in the water at a faster rate.

This being said, we do water changes for the fish. To remove impurities that our bio systems don't and replace micro nutrients which the plants steal. Regular water changes will put less stress on our fish after some time due to the adapting capabilities of a living organism. To explain the difference between weekly water changes and a massive water change every 3 or 4 months I want to use the next example. We can take a fish from the purest amazonian waters and gradually make it used to the hardest nastiest tap water on earth and that fish will flourish. Take that same fish and dump it in a bucket of straight out of the tap water and its dead in a day.

 

This is a very interesting read! IMHO this is the direction all aquarists should pursue. More sustainable fish keeping, less mandatory maintenance - i.e. les chance for our inadequate or lack of maintenance to result in poor/harmful conditions. Having said that, we will never truly ever be rid of water changes due to the requirement to replenish micro nutrients. I think it has been mentioned lots of times before - a stable environment is more important than attaining perfect water parameters. So regular water changes are crucial.

I agree with it all. Beyond a certain point, increased filter area being it a sump or a HOB will only increase the efficiency with which ammonia and nitrites are converted into nitrates. The only thing affecting the amount of nitrates will depend on your stocking levels and feeding regimes vs what you take out with water changes and nitrate scavengers like plants. The residual amount of nitrates will tend to stabilise to some constant value over time. This value will be unique to your tank based on your water change regiment and bioload.

I've tried to develop a model to estimate cycling times of new tanks based on their volume, flow rates, bioloads etc. on MASA. The unknowns makes it very difficult to determine the exact nitrate concentrations over time... Need more experimental data.

 

Plants prefer NH3 and NO2. Numerous articles on this. NO3 is the most stable. I assume you just got them mixed up:wondering:

Measure your NH3 (ammonia) and NO2 (nitrates). They should be 0 in a healthy system. If they are not you need a better filter system (bigger, faster, more efficient take your pick)(and your fish are at a real risk and nitrate build up is your least worry). Once you have a tank with 0 NH3 and NO2 your bio filter is working. Doing anything more will only be wasted money and effort. Possibly a mechanical filter will help make the water clearer. Ofcourse a bigger filter will be insurance against ammonia spikes and such.

Removing NO3 occurs by a) water change (most effective). b) anaerobic filter c) plants (least effective) d) Prime or similar (not practical and expensive). A normal planted tank has miniscule impact on nitrates.

 

What are micro nutrients?

 

Phosphorus (P), Carbon, Potassium (K), Magnesium (Mg), Calcium (Ca)

Very important if you want proper plant growth.

 

Those are actually called macro nutrients, as they are used in greater quantities by the plants. The micro nutrients are things like iron, molybdenum, strontium and copper. There are many others, but they are called micro nutrients because plants only need these in trace quantities. That does not make them less important though...

 

Yes sorry now that I actually read through my post I see the mistake. Thanx for pointing it out

 

OK, I add a discus muti that has micro nutrients.

Back to maths. For every 1 gram of nitrogen processed in your filter it require 3.6 grams of oxygen!!! So adding a few airstones to the filter will make it that much more efficient!!

 

And the higher the temperature in a filter the more efficient it is.

 

@Biggles but what about the anaerobic bacteria don't they need oxygen to operate. So if the water temperature is too high you lesson the amount of oxygen in the water.

 

Hence the reason for adding oxygen manually. I have found with my filter that the right ratio works just as well. I use only bio media with high porosity and 2 mechanical trays. In my filter floss tray I have a purigen bag for chemical filtering. More bio media surface means exponential increases in bacteria quantities which boils down to a perfectly efficient filter.

 

As I understand warmer water holds less oxygen. And anaerobic bacteria's lack of oxygen tolerance is pretty low, which means if there is not adequate flow or oxygen they start dying making the whole process go balls up.

 

@Swagasaurus Yes it is true and I forgot to mention that I run my setup at a standard 27 deg. When you go higher with the temperature ie. 30deg or more you need to add oxygen to the filter with an air stone

 

@Swagasaurus @Double-D Normal filter bacteria are aerobic, meaning they use oxygen, so as I mentioned they use a lot of oxygen to metabolise ammonia and nitrite. Having an airstone in the filter is a big plus or having you filter media exposed to the air. Splashed on an overflow or balls floating near the surface. I have 2 airstones and all my heaters are in the biofilter section of the sump.

Anaerobic bacteria that metabolize nitrates do not use oxygen, in fact oxygen will kill them That is why it is such a mission to set up an anaerobic filter and it doesn't form part of the normal aquarium filter system.

My discus sit cosy at 30C in the main tank so I need a lot of aeration anyway. I am sure my most productive bio filter is teh bag of balls that sit on the overflow of the display tank. They are wet but not submerged.

 

Misread that bit :banghead: But yes my posts was aimed at aerobic bacteria