Build up in planted tank

[zin]

this is probably just a concept im not understanding but,

when i do a 50% water change weekly, that leaves 50% of the water, cant the concentration of certain chemicals build up in whats left to lethal points? ie CU?

if that doesnt make sense ill try another way. (no meaning to the numbers ><)

1ppm of something in the tank, 50% water change, then there is .5ppm, you end up adding 1ppm from ferts over the week, then theres 1.5 ppm, 50% water change, then .75ppm. and so on...

or am i missing something?

or maybe just a real reason i, and others, do 90%ish water changes every now and then instead of the usual 50%

[her209]

Yes, this leads to Old Tank Syndrome.

[RTR]

Except that the plants supplements you have added should have been dosed such that you would expect more than 50% of the material to have been taken up by the plants during the week. Otherwise you are likely overdosing.

But planted tank or not, periodic larger scale changes are highly beneficial IMHO to purge most of the dissolved organics which we cannot test easily if at all.

[zin]

do plants use any cu?

iv always heard of it being unneeded and simply impurities in ferts?

anyway yeah i was just curious, big water changes every now and then seem to be the way to go

[RTR]

Copper is a required micronutrient. Whoever you heard from was mistaken.

[anonapersona]

Originally posted by zin
[B]1ppm of something in the tank, 50% water change, then there is .5ppm, you end up adding 1ppm from ferts over the week, then theres 1.5 ppm, 50% water change, then .75ppm. and so on...

or am i missing something?


I've seen it proved mathematically that the concentration will reach X/Y where X is the ppm of the dose and Y is the % water change as a decimal....

add 1 ppm and change 50% >>> 1/.50=2ppm

Somewhere on the Krib, you'd have to search to find the original info.

[zin]

i dont even know who i heard it from,
i guess i got it wrong

i guess im looking for more info on copper, iv heard of it being lethal at small levels...

i know all traces or most can be lethal at higher concentrations, but i heard copper can build up quick

anona- il look for that, sounds like a interesting read

[zin]

found it

http://www.thekrib.com/Chemistry/h2o-changes.html


pretty interesting

[RTR]

Copper does not stay in solution long in other than quite acid tanks, it plates out in/on the substrate. the only way to build it up would be chelation, and that may or may hold it. Iron, copper, the other metalic traces are hard to keep in the water - they are normally chelated in trace element solutions, but even that is not long lasting. You cannot count on the trace elements, especially the metals, staying in solution in any form for days, much less weeks. They are either consumed by the plants or lost to insoluble forms.

You need to some background reading on nutrient requirements and dosing. The Krib can be very confusing and lead to information overload, but most of the info is there. Alother good source is the APD archives:

http://fins.actwin.com/aquatic-plants/

[zin]

i dose traces and iron daily, P N K 2x a week,
No3~10ppm P~1ppm K~15ppm

was just curious about the build up more or less with the 50% water change..