Over Fert Question - The Planted Tank Forum
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post #1 of 3 (permalink) Old 07-23-2006, 01:04 AM Thread Starter
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Over Fert Question

This is for all those very experienced people here.
I have nearly 4 1/2 wpg with a very high plant load. It is a 29 gal tank in question.
I increased my ferts for a 35 gal tank instead of a 29 gal. The plants seem to be growing faster. But I am starting to get green water. Does over fertilizing cause algae or GW? Does adding to much Iron effect algae or GW? I started adding extra Iron Chelates at 1 gram for a while and then 2 grams for a while and now I am up to 3 grams.
I dose Greg Watsons Ferts EI method and have high C02 through DIY.
kno3 - 1.9 grams
k2so4 - .9 grams
kh2po4 - .6 grams
csm+b - .4 grams on off days
fe - 3 grams on off days
Because of all the incorrect test kits I rarely test.
Thanks for any help.


10 gallon hospital tank.
29 & 50 gallon - High Tech C02 enriched.
50 gallon Pond - Natural.
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post #2 of 3 (permalink) Old 07-23-2006, 02:17 AM
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It is very hard to avoid algae with 4.5 watts per gallon on a 29 gallon tank. And, the higher the light and the faster the plants grow the more fertilizer you need to keep up with the growth. If you are low in phosphate the plants can't use the nitrates nearly as well, so it's the same as a shortage of nitrate. Green water, tends to start with an ammonia spike which could start from disturbing the substrate, allowing a plant tab in the substrate to be exposed to the water, a dead fish allowed to rot, too many dead leaves rotting, too much fish poop, etc. And, since a drop in CO2 ppm during the day can also trigger algae to grow, I doubt that DIY CO2 will work consistently with that much light. So, the simplest solution is to turn off about half of the lights, do a blackout to kill off the green water, do a water change and filter cleaning to get rid of the dead green water algae.

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post #3 of 3 (permalink) Old 07-23-2006, 07:20 AM
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DIY CO2 + high is a very bad combo.
A good filter, good routine cleaning of the filter, will help to some degree.

But with high light/nuttrients, then you stop adding CO2 for a bit, that also induced GW in several tanks I tested.

Less CO2=> less N uptake.
This may result in more NH4 loading (this NH4 load remains unchanged(the rate of loading into the tank). But the rate of NH4 uptake is regulated by ther carbon supply to some degree, thus is downregulated by the plant's uptake enzymes when less CO2 is available and in a limiting amount.

That's the simplified version.
The molecular version is much more involved.

For plants:
The potential toxicity of elevated ambient concentrations of NH4+ severely limits the range of concentration over which adaptation is possible. NO3, this is not the case, it can possess a much wider range of concentrations.
NH4+ disspates transmembrane proton gradients that are needed for photosynthesis and respiration electron transport.

The plant has much less leeway here with respect to NH4+.
What regulates the acqusition of NH4 with respect to CO2?
What carbon backbone is required to make glutamate? The precursor to glutamine? NH4+ is the precursor to Glutamine.

If the TCA cycle, the cycle supplying the carbon to the plant, is reduce by reducing the CO2 supply.............anything that disrupts the production of Glutamate or it's precursors will secondarily disrupt the assimilation of NH4, which in turn tell the NH4 uptake enzyme to stop taking in NH4 since there are less Carbons than are needed to forum glutamine.

So if you have a steady rate of NH4 being removed via plants/bacteria, then you do something under high light/nutrients to disrupt the bacteria/plant's uptake, then you have a back up and elevated levels of NH4.

Note, a small change in NH4+ levels in the water column causes a much more sensitive response than NO3 might.

I shut off my filter to an otherwise well run tank, high light, EI etc. And added a similar flow pattern and flow rate for the tank with a powerhead, I got greenwater within 30 hours.

I just did this 3 days ago.

I tried this with lower CO2 some years back, this produced a relapse of GW blooms after a few days past the the last UV sterilizing treatment.
Adding enough CO2 did not induce the GW bloom back again thereafter, but the sub optimal level of CO2 did induce a bloom.

You can try these ideas out and see if you can find similar experiences.
You can also add inorganic NH4, or urea, or organic forms of reduced N and see if you get GW(you should) at fairly small ranges.

Then kill the GW with the UV and try it again.
Note: such test tend to only hurt the Algae, the plants typically do fine/very well.

Tom Barr

Tom Barr
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