Water Changes

[KittyKat]

Reading another thread about plants and water changes,say you need to do 50% a week in a full planted take? is this only for people with co2 and using fertilisers etc? and with low tec plants, you only do top ups water changes to get the fish waste etc to turn in to the fertilisers? please can some one explain, why some people do 50% or more a week and others only do little or top ups. Your advice will be most welcomed

From what I understand, this is for tanks where one overdoses on the fertiliser, so water changes are needed to remove excess left-overs or it would just accumulate to the point where it will harm fish and plants.

Lots of folks reiterate this but its actually due to the increased production of metabollic waste from the plants in CO2 enriched tanks.

This explanation is plausible and realistic, so I am relatively happy to go with that. I will still brand it under "overdosing" though, as it is caused by higher amounts of fertilisation than the tank can sustain.

You even see this in EI articles but it's nothing to do with resetting the nutrient levels because after all we have nothing to fear from them.

Disagree, constantly high levels of certain metals and "nutrients" can, and do, harm certain species of fish in the long term. So without the water changes, I expect that it is possible for these to build up to dangerous levels.

 

[RadaR]

What is high? Could we ever reach these levels in high tech tanks which need to be dosed frequently otherwise we run out?

No3 Dosing Toxicity For Fish/shrimp

Copper I agree is toxic to shrimp but the concentration in trace element powders is small because after all these minerals are only needed in trace amounts.

On average, you are looking at getting Nitrate 20–30 ppm, Phosphate 1-3 ppm, Potassium 20-30ppm per week in an EI tank which is one of the least lean methods. Assuming that none of these nutrients are used up by the plants then it would still take 4 weeks for the NO3 concentration build up to dangerous levels for shrimp.

 

[SO19Firearms]

I will still brand it under "overdosing" though, as it is caused by higher amounts of fertilisation than the tank can sustain.

If I understand you correctly, i don't think that's quite correct - In theory you could add just the right amount of ferts so that every aspect of the N,P,K + all trace elements are used up by the plants

- But you'd still need to do the water change regardless of all the readings (presuming the readings can be measured accurately) being at Zero....because of the plant wastes.

 

[KittyKat]

What is high? Could we ever reach these levels in high tech tanks which need to be dosed frequently otherwise we run out?

As far as I am aware, yes, if dosing to the higher amounts that some people do.. I'm not even trying to imply that it is the case for all "high tech" set ups, but it probably is for a minority. If you have access to journals, I can try and find a few papers with more details.

I will still brand it under "overdosing" though, as it is caused by higher amounts of fertilisation than the tank can sustain.

If I understand you correctly, i don't think that's quite correct - In theory you could add just the right amount of ferts so that every aspect of the N,P,K + all trace elements are used up by the plants

- But you'd still need to do the water change regardless of all the readings (presuming the readings can be measured accurately) being at Zero....because of the plant wastes.

What exactly do you mean by "plant wastes"? Ammonia? Rotting plant matter? Something else?

In theory, dosing perfect amounts should work very well, but in practice, it's impossible to do that. By perfect amounts, I mean those which the plants will use up completely, but which will not, for example, result in too much ammonia being produced by rotting plants or plants growing so fast that they use up too much oxygen, etc. So in that case, there should not be any need to remove anything from the water.