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EI and water changes

Tim Harrison

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What is the general consensus of opinion out there regarding the use of the frequent and large water changes employed by eutrophic dosing methods such as EI. Is it to rid the tank of the supposed build up of metabolic waste products of plants, due to elevated rates of photosynthesis, or is it to reset nutrient levels to prevent build up thereof? Or none of the above?
 
Thanks for that, but I am still a bit puzzled, though. Although I am sure you are right to an extent it doesn't necessarily explain the disproportionately large water changes (50% or more per week) typically advocated by such methods as EI?
 
EI is a fert regime therefore the only reason for large, regular water changes is to reset nutrient levels to prevent build up thereof.

The basic principle of EI is to always provide more ferts than the plants can consume. Thus to prevent build up to toxic levels a reset is required.

However as a added bonus of EI by doing the water changes you also reduce the build up of metabolic waste products of plants, due to elevated rates of photosynthesis.
 
However as a added bonus of EI by doing the water changes you also reduce the build up of metabolic waste products of plants, due to elevated rates of photosynthesis.

Hi thanks for confirming that. It's as I thought, however, I do struggle a bit when it comes to this whole thing about metabolic waste products of plants. I would be very curious to know what these waste product are exactly, and how they come to be secreted, and by what mechanism etc.

I may be over simplifying things a bit but isn't the primary waste product of photosynthesis O2? And don't plants store all the other products of photosynthesis in vacuoles for later use, as food, and to convert into chemicals for defence against herbivory, and to inhibit algae and other plants etc?
 
Hi,

I believe that plants (maybe not all) do secrete substances other than O2. Chemodefence against predators or even agaist other plant competitors is a common thing in natural ecosystems.

I know that marine brown algae such as fucoids have lots of secondary metabolites that are used against herbivore grazers such as littorinids. I also know that some Acacia trees use these substances against herbivores (giraffes) in the African plains. I would imagine that the plants we use in our tanks are no different.

Just my two pence,

GM
 
I have no scientific evidence or explanation, I have read several thousand threads on various forums though! :?
It would seem that regular large water changes are effective, whatever the reasons.
I could say that this only seems to apply to high energy tanks with fast growing plants & with lower light, non C02 tanks not requiring or perhaps needing, the large water changes - or so I read.

From my own personal experiences, I know for a fact that if miss two consecutive water changes, algae will appear & may take a month to disappear.
I agree it would be nice to know the true scientific reason why the large water changes are so effective?
 
Thanks guys for taking the time to share your thoughts

From my own personal experiences, I know for a fact that if miss two consecutive water changes, algae will appear & may take a month to disappear.

I think that the above could perceivably be used as evidence to support the supposition that disproportionately (and the key word is "disproportionately") large water changes, typically 50% or more, advocated as part and parcel of eutrophic dosing methods such as EI are to reset nutrient levels, to prevent build up thereof, and the subsequent imbalances that can kick start algal blooms, for instance.

I believe that plants (maybe not all) do secrete substances other than O2. Chemodefence against predators or even agaist other plant competitors is a common thing in natural ecosystems.

Undoubtedly, they also remove the toxic substances of fish respiration as well, but as for plant secretions, I am afraid I remain very sceptical. I doubt that even under accelerated photosynthesis substances such as allelochemicals will be produced in sufficient quantities to impact on an aquarium, especially in the space of a week or so.

Further, it is possible to tweak EI to a point where the input of nutrients can be reduced to a minimum whist still providing non-limiting nutrient availability to plants. This in turn means that you can reduce water changes from say once a week to once every two weeks or more. Surely this is further evidence that the disproportionally large water changes are to reset nutient levels and not to remove the toxic products of fish or plant metabolism, should the latter exist? If they were to remove toxic products of metabolism wouldn't a weekly water change, of say 15% to 20%, be sufficient?
 
Hi
Do very little water changes and gravel cleaning when your dosing Co2 and supplementing fertilizers and you will see the results in a few weeks. o_O
The evidence will be before your eyes.....and it wont be that pleasing.
Remember you are trying to replicate the flow of a stream,river or lake where the build up of excess materials are dispersed/removed continuously....by the local means necessary to cleanse the natural habitat.
Cheers
hoggie
 
Hoggie, I always thought gravel cleaning was discouraged with planted aquariums, what issues can it cause? I don't want to find out myself :lol:
 
Another observation - withing an hour after lights on, after a large water change, the plants will pearl like no other day.
I believe this to be due to the additional C02 contained in the fresh tap water?

Hi, I don't think they pearl because the tap water contains a lot of co2. It is more because the tap water contains a lot of oxygen and when you pour the water into the tank, you oxygenate the water more. Because the tank then has a much higher oxygen content, the water is then at saturation point with oxygen, hence the pearling.
When I do my weekly water change, my drop checker goes from a dark green to blue. If the tap water had a high CO2 content, then the drop checker would go more green after a water change, not blue.
 
Do very little water changes and gravel cleaning when your dosing Co2 and supplementing fertilizers and you will see the results in a few weeks.
The evidence will be before your eyes.....and it wont be that pleasing.
Remember you are trying to replicate the flow of a stream,river or lake where the build up of excess materials are dispersed/removed continuously....by the local means necessary to cleanse the natural habitat.
Cheers
hoggie

I was wondering then, how do low energy lacustrine environments and other standing water bodies such as ponds with very little if any water movement fit that theory? I always thought that it was the macrophytes themselves that cleansed the water rather than adding further waste products? And why then have purpose built wetlands been used as sinks for purifying water for decades? Just curious.
 
Do very little water changes and gravel cleaning when your dosing Co2 and supplementing fertilizers and you will see the results in a few weeks.
The evidence will be before your eyes.....and it wont be that pleasing.

Could it be that what aquarists are actually witnessing, in their higher energy tanks at the end of the week, is the effect of an unhealthy imbalance in excess nutrient levels due to eutrophic dosing and preferential nutrient uptake?
 
What I see in my tank every day, are the plants pearling or producing bubbles from the leaves & stems, what I see after a large water change is a lot more of the same effect?

That could fit with my theory since a water change will reduce the effect of any imbalance and kick start photosynthesis anew, especially if they start to pearl, or pearl even more, after the first subsequent nutrient dose.
 
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