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Fert uptake speed


28 Dec 2007
North Wales
Sorry if this has been answered elsewhere already, but I was wondering when fert dosing , how soon after adding ferts to the water column, are the nutrients absorbed and used up by the plants? Is it a mattter of minutes or hours? Or is it impossible to measure? Obviously there are a lot of factors involved such as, what type of plants you're feeding, lighting levels etc. Could you in theory dose several times a day? or would that just encourage algae growth? Sorry for all the questions, just feeling inquisitive this morning. :rolleyes:
Hi Martin,
From what I gather as soon as the lights go on the machinery of photosynthesis begins, although the uptake rate will not be at it's nominal value for an hour or more. As you noted, it all depends on the amount of light, the CO2, substrate etc so don't hold me to the numbers.

You can dose as often as you wish, but why would you want to? The idea is to make things more simple, not more complicated. Nutrients don't encourage algae, ammonia does. If you dose an inadequate amount such that there is a deficiency at the time when the plant requires uptake, then the plant will suffer and that will encourage algae growth.

Thanks for the reply ceg, your opinions are appreciated and I agree that this planted tank lark doesn't need to be made anymore complicated than it already is! one more query, is it possible to overdose the plants with ferts or would I end up with aquatic triffids!
Assuming that your lighting levels are proper, that your tank maintenance is in order (such as water changes, filter cleaning, detritus removal etc) and that your CO2 levels are proper (if used) then an overdose of nutrients is simply wasteful and can generate plant growth rates that require more maintenance such as trimming, leaf removal and so forth. "The Day of The Triffids" would come only if you had very high lighting and very high CO2 in addition to the nutrient overdose. If any of these other parameters are limited, which is often the case, then the extra nutrients do nothing positive.

Many people operate at lower nutrient levels to control growth and to also curtail the algae "propagation" rate in case algae does form.

Additional info:
Overdosing nutrients can neither harm you plants nor you fish and they cannot not induce algae. There is a catch though - once algae infests your tank, for reasons such as unhealthy plants or other ammonia/light reasons, then the algae that forms will immediately start feeding on whatever nutrients are currently in the water- so the algae multiplication rate becomes high in the presence of nutrients and phenomenal where there is an overdose of nutrients. This often gives the illusion that it was the nutrients that caused the algae. There is a lot of confusion on this issue.

Always remember that depending on light intensity, the ammonia concentration level required to induce an algae bloom can be 10 to 100 times less that what your ammonia test kit records as "zero" :wideyed:

Hope this helps.