Fertilizing a 65 Gal low-medium light tank - The Planted Tank Forum
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post #1 of 15 (permalink) Old 02-20-2016, 04:03 AM Thread Starter
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Fertilizing a 65 Gal low-medium light tank

Today I bought a new API nitrate test kit, primarily because I had a plastic envelope filled with what I thought was KNO3, and my working supply of KNO3 is near zero. With that kit I measured the nitrate in my tank water as it is today, between 10 and 20 ppm. I canít distinguish the colors any closer than that. I measured my tap water, which should have near zero nitrates, and it is zero. Then I mixed a tiny bit of my supposed KNO3 in a glass of tap water, and measured that, getting over 60 ppm of nitrate, so it really is KNO3.

Iím posting this to show how I decided to fertilize my tank, after a lot of thought triggered by Marcelís threads on the subject. This is the first time I have done any serious thinking on this subject, so I thank Marcel for ďturning me onĒ with his posts.

I have a 65 gallon tank, which contains about 56 gallons of water, due to the substrate taking up part of the volume. Based on reading some of Tom Barrís articles in his Barr Report, on the internet, plus Edwardís PPS Pro recommendations, and Marcelís test results, I want to have about 15 ppm of nitrate in my tank water. This is because the uptake of nitrates by the plants is partly determined by the concentration of nitrate in the water, and my desire to have enough to discourage blue green algae (BGA). I donít want the concentration to increase between my water changes.

The three references above say the daily uptake of nitrate for a heavily planted, high light, high CO2 tank, with good nutrient levels, is from .1 to .7 ppm. My tank is moderately heavy planted, perhaps half of ďheavily plantedĒ, so that will reduce the uptake of nitrates to about .05 to .4 ppm. I doníít use CO2, but I do use Metricide for a carbon source. And, my light intensity is low medium, around 40-45 PAR, with my Finnex Planted Plus located about 23 inches above the substrate. This should reduce the uptake to about 1/3 to 1/4 of what it would be with high light and CO2. (Iím assuming my plant growth rates will be between 1/3 and 1/4 of what they would be with high light and CO2). Based on that my daily uptake of nitrates should be about .01 to about .15 ppm. I will assume that .1 ppm is the best estimate.

In 7 days, my 15 ppm of nitrate should drop to about 15 - (7 x .1) or to about 14 ppm. Clearly, I wonít need to dose nitrates more often than weekly. Assuming I do 50% water changes every 2 weeks, as I want to, I really donít need to dose any nitrates during that 2 weeks, and the nitrate level should only drop to 13 ppm, and even if the uptake is .7 per day, in 2 weeks the level should only drop to about 5 ppm, which is acceptable to me, but unlikely to actually go that low.

My fertilizing plan will be:
Dose enough KNO3 after each 50% water change to raise the diluted tank water nitrate concentration back to about 15 ppm.

The next most critical fertilizer element is potassium. If I have 15 ppm of nitrate, I also have 9.5 ppm of potassium, the ďKĒ part of KNO3. But, I want at least 15 ppm of potassium, primarily to prevent it from being the limit on plant growth. I will need another source or sources of potassium. My phosphorous will come from KH2PO4, which contains 40% as much potassium as phosphate (PO4). That will be one source, and, for now KCl will be the other source.

I want 3 ppm of phosphate in the tank water, primarily to try to avoid Green Spot Algae (GSA), which my experience shows will not appear if I have relatively high phosphate. The plants only need around 1 ppm, so 3 ppm should be enough, and should not be a toxic level. If I have 3 ppm of phosphate I will have .4 times that added potassium, or about 1 ppm. This will leave me 4.5 ppm short of the 15 ppm I want, so I will use KCl for that.

Daily uptake of potassium and phosphate should be approximately proportional to the daily uptake of nitrate and the starting concentration of phosphate or potassium compared to that of nitrate. So, if I donít need additional dosages between water changes of nitrates, I also wonít need additional dosages of the other nutrients.


Trace elements are going to come from dosing Millerís Microplex, and chelated iron just because I have lots of them. I will dose the Millerís Microplex to get .5 ppm of iron, and add enough chelated iron to get to about 1 ppm total iron.

Using the fertilizer calculator at Aquarium Nutrient Calculator my post water change dosages will be:
KNO3 - 10 ppm NO3 6.5 ppm K - 11/16 tsp
KH2PO4 - 2 ppm PO4 - .7 ppm K - 3/32 tsp
KCl - 3 ppm K - 7/32 tsp
Millerís Microplex - .33 ppm Fe - 5/16 tsp
Chelated Iron (10% I think) - .33 ppm Fe - 1/8 tsp

Some of these dosages are going to be very hard to measure at all accurately, so I will use my 16 ounce dosing bottles, which have a 1 ounce dosage chamber. One bottle will have the macro nutrients and the other the micro nutrients. To figure out how much of each chemical to put in the bottles, I will put 16 times the one dosage amount, and fill the bottle with 16 ounces of tap water. These mixes should last me 32 weeks - 8 months!! For that to work I think I will have to add some Metricide to the micros bottle to stop any microscopic life from growing.

I welcome any suggestions about changes I should make.

Hoppy
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post #2 of 15 (permalink) Old 02-20-2016, 04:35 AM
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A couple of suggestions Hoppy.

Dose the water change water before adding to the tank at water change. This will make the water going into the tank virtually exact to the water having been taken out. There'll only be a slight increase in nutrient concentration (in the water change water) to cover off plant uptake.

SO4 has far more value to a freshwater planted tank then Cl. Consider hitting your K target with K2SO4 rather then KCl. Perhaps a better description would actually be, SO4 concentration can be significantly higher then Cl before problems arise. If this isn't an option, look for salt burn on leaf edges which I've found Cl to be responsible for.

IMO, you have the trace ratio way to high. I am at around 8 ppm N (35 ppm NO3), 1.5 ppm P (4.5 ppm PO4), 20 ppm K, with the following trace concentration.
Fe 0.1786
Mn 0.0435
B 0.0067
Zn 0.0071
Cu 0.0041
Mo 0.0018

My trace deficiency symptoms seem to resolve themselves at Fe 0.15 ppm (other trace elements proxied against Fe). I've only bumped the dose a little higher to ensure I have the required concentration covered off. I would consider my system to be medium (maybe medium-high) planted, high light (two T5HO 54w + two T8 18w, 12 hour photoperiod, around 15" from substrate), medium CO2 (best guess 15ppm, maybe a little higher rather then a little lower).

Dose the trace solution in the smallest doses possible, as often as possible. Once a week is better then once a fortnight. Every other day is better then once a week. Every day is better then every other day. Whatever you feel comfortable with.

If at all possible, keep all of the nutrients in separate dosing containers. By putting all of the macros in one solution bottle, the ratio between the macros is locked by that solution bottle. By keeping the macros separate, you open the possibility of adjusting each macro solution individually and easily. By putting everything in the one solution container, if you decide you need more or less PO4, you also have to increase or decrease K, NO3, Cl/SO4 by the same percentage that you increase/decrease PO4, or start dosing PO4 separately, or make a new solution mix.

Once you become acclimatized to what your tank requires, then you can lock the nutrient mix in to one solution bottle and reduce manual tasks.

Feel free to edit.

Last edited by Audionut; 02-20-2016 at 04:47 AM. Reason: Dosing less trace elements more often
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post #3 of 15 (permalink) Old 02-20-2016, 05:04 AM Thread Starter
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I change water with a hose attached to the kitchen faucet, so I can't add anything to the water as it goes in. We all have to evaluate our commitment to our hobby, and the amount of time and work we will be willing to do on a continuing basis. Then we can select our type of tank to be compatible with that. I'm a low light, low time commitment, type of hobbyist! That is why I selected a modified EI type fertilizing method. I may test my nitrate concentration occasionally, but it is highly unlikely that I will ever want to tweak the dosages very much.

I want to have as high a nutrient concentration as I can, without risking toxicity, so I don't want to dose daily or even 3 times a week unless it is essential, and it appears that it definitely isn't. That is true for traces as well as macronutrients. When I first started this hobby I enjoyed every minute I worked on my tank, so I had high light, pressurized CO2 and all of the maintenance that required. Now, I'm not like that anymore.
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post #4 of 15 (permalink) Old 02-20-2016, 05:32 AM
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Quote:
Originally Posted by Hoppy View Post
I want to have as high a nutrient concentration as I can, without risking toxicity, so I don't want to dose daily or even 3 times a week unless it is essential, and it appears that it definitely isn't. That is true for traces as well as macronutrients.
I would highly suggest you research chelating substances a little more thoroughly. The chelate protection of metals will not last anywhere near two weeks. Once the chelate breaks down in the first few days, the metals are very likely to precipitate, or worse, accumulate, resulting in no availability/toxicity of trace elements.

Once precipitation happens, you'll be entirely reliant on stored supply in the plants and what little amount becomes available through biological processing. If you stick to your current trace dosing routine and concentrations, I can all but guarantee one or two things will happen.

The growth rate of the plants will reach a point that is greater then the available supply. Just because you add some concentration of trace elements into the water doesn't guarantee their availability. This is actually the best case scenario, because it will force you to consider what your tank needs, rather then what you prefer doing. Although having said that, adding more rather then adjusting the manner in which you dose only leads to issue number 2 below.

The supply of available trace elements will meet demand from the plants. This might seem fine, but you will hit a point where the supply of metals reaches a point where it causes problems. I can't emphasize enough just how much of those trace elements you want to dose, won't actually be available to the plants. Less is more Hoppy.

edit: My numbers for EI low light = an accumulated concentration of 0.4 ppm Fe.
Millers microplex is heavy on Cu. The calculator you listed in the OP even shows a warning message from a 0.2 ppm Fe dose of MM.

Feel free to edit.

Last edited by Audionut; 02-20-2016 at 07:55 AM. Reason: Millers is Cu heavy
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post #5 of 15 (permalink) Old 02-20-2016, 04:38 PM Thread Starter
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Thank you Audionut! I learned something new to me. So, chelated metals have a much more limited life in the tank than I was aware of. That does make me rethink this. I will take a short break and do some more research on that subject.
EDIT:
Why does the chelator break down in the tank, but not in the bottle of trace element pre-mix?
EDIT:
About K2SO4 vs KCl, with the dosage of KCl I plan to use, and 50% water changes before each dose, my maximum buildup of Cl is less than 2 ppm. I found a couple of references for toxicity of Cl to aquatic plants that place limits of 150-230 ppm for Cl in water with plants growing in it. So, I should not run into Cl toxicity.

Hoppy

Last edited by Hoppy; 02-20-2016 at 06:52 PM. Reason: Add more info
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post #6 of 15 (permalink) Old 02-20-2016, 07:55 PM
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I use tetra plantamin, which claims to work for 4 weeks and does provide iron.
Seems to work, other than a slight nitrate deficiency, my tank's seem to do ok.
It contains no N or P. It is mostly trace elements and iron.

It may be because I dose half recommended amount, twice as often.

Cape Town, South Africa.

Hi. I'm back.
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post #7 of 15 (permalink) Old 02-20-2016, 08:43 PM
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@Hoppy
Let me know what you decide to dose.
We have similar setups and this would help me alot
Thank you for researching this!!
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post #8 of 15 (permalink) Old 02-20-2016, 09:27 PM Thread Starter
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Quote:
Originally Posted by Audionut View Post
I would highly suggest you research chelating substances a little more thoroughly. The chelate protection of metals will not last anywhere near two weeks. Once the chelate breaks down in the first few days, the metals are very likely to precipitate, or worse, accumulate, resulting in no availability/toxicity of trace elements.
From what I have been reading EDTA, the chelator in CMS+B, is not easily degraded. Nothing I found indicated that it will degrade in a few days, unless bacteria is introduced in sufficient concentration to degrade it. Do you have a link to something that indicates otherwise?

Quote:
Originally Posted by Hoppy View Post
Why does the chelator break down in the tank, but not in the bottle of trace element pre-mix?
I found this, https://www.plantedtank.net/forums/11...premixing.html which seems to answer my question. Is it the presence of phosphate ions in our tank water that causes the breakdown of chelated metals?

Quote:
Originally Posted by Hoppy View Post
I have a 65 gallon tank, which contains about 56 gallons of water, due to the substrate taking up part of the volume.

For trace elements:
Miller’s Microplex - .33 ppm Fe - 5/16 tsp
Chelated Iron (10% I think) - .33 ppm Fe - 1/8 tsp

Some of these dosages are going to be very hard to measure at all accurately, so I will use my 16 ounce dosing bottles, which have a 1 ounce dosage chamber. One bottle will have the macro nutrients and the other the micro nutrients. To figure out how much of each chemical to put in the bottles, I will put 16 times the one dosage amount, and fill the bottle with 16 ounces of tap water. These mixes should last me 32 weeks - 8 months!! For that to work I think I will have to add some Metricide to the micros bottle to stop any microscopic life from growing.

I welcome any suggestions about changes I should make.
Given that chelated metals (chelated with EDTA), cannot be expected to remain available to the plants for more than a day or two, at most, I will change to dosing these in a liquid pre-mix form, every other day between bi-weekly water changes. To avoid over dosing copper, and still get adequate iron, I will use iron chelate (EDTA) for 80% of the iron, with the remainder and the rest of the traces coming from Miller's Microplex.

Miller's Microplex - .05 ppm Fe - 3/64 tsp
Iron Chelate - .2 ppm Fe - 1/16 tsp

I will use a dosing bottle, with 14 ounces of water, and 14 times each of the above dosages, and dose 1 ounce every other day. This seem pretty low to me, but maybe it isn't. This pre-mix will only have to remain usable for 4 weeks, so deterioration shouldn't be a problem.

If this is my final decision, I plan to do a 50% water change Tuesday, so this is when I will need to have this ready to use.

Hoppy

Last edited by Darkblade48; 02-21-2016 at 08:25 AM. Reason: P
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post #9 of 15 (permalink) Old 02-21-2016, 07:48 AM
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https://en.wikipedia.org/wiki/Ethyle...ic_degradation

Quote:
The most important process for the elimination of EDTA from surface waters is direct photolysis at wavelengths below 400 nm.[25] Depending on the light conditions, the photolysis half-lives of Fe(III)EDTA in surface waters can range as low as 11.3 minutes up to more than 100 hours.[26]
Wikipedia contains some citation. I can't find the link I had with good info regarding EDTA. @Marcel G has done some testing too. I believe he has some results in one of his threads.

Feel free to edit.
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post #10 of 15 (permalink) Old 02-21-2016, 10:11 AM
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Iron chelates little testing

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post #11 of 15 (permalink) Old 02-21-2016, 01:38 PM
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If I remember correctly @Marcel G, you found some relationship with light and heat also?

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post #12 of 15 (permalink) Old 02-21-2016, 01:55 PM
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Thanks God for the fridge!

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post #13 of 15 (permalink) Old 02-21-2016, 04:31 PM Thread Starter
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Yes, I found references to light breaking down Iron Chelate, but only light in the UV and near UV range. None of our typical aquarium lights produce more than trivial amounts of light in that part of the spectrum. And, sunlight inside our homes has very little UV, if any in its spectrum.

On the other hand, when I previously used liquid pre-mixed trace mixtures the color of the liquid would change from green to brown, over about a 2 week period, leaving my dosing bottle stained brown. That suggests to me that the mix was breaking down pretty quickly. The dosing bottle is polyethylene plastic, milky white, and is stored in the dark under my tank cabinet. I never found mold growing in the mix, so I never did refrigerate it.

I think it is prudent to assume our trace elements need to be dosed much more often than weekly. So, I will go ahead with my plan in post #8, except I may decide to modify it and dose traces daily.

EDIT: I mixed up my dosing solutions. The macros all dissolved, but the water was warm, so I don't know if any will come out of solution as it cools. The traces I decided to dose daily, but the same dosages as I listed above. Those dissolved with no question. And, I dosed my first ounce dosage this afternoon. My fingers are crossed!
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Last edited by Hoppy; 02-21-2016 at 10:23 PM. Reason: Add more info
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post #14 of 15 (permalink) Old 05-09-2016, 04:03 AM Thread Starter
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Almost 3 months later:
The biggest change I have seen in my tank is that now I get green algae on the glass much faster than I used to. The next morning after a cleaning, 50% water change, and dosage of fertilizer, the glass is already a bit hazy with green algae. It isn't typical green dust algae, just the green algae that eventually grows on the glass in most aquariums. So, I think my experiment is a flop! My plants haven't done any better than when I was just haphazardly dosing, if they are even doing as well.

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post #15 of 15 (permalink) Old 09-06-2016, 10:04 PM Thread Starter
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UPDATE: Since my last post, when my plants were largely just existing and not growing much at all, I added DIY CO2, at a low bubble rate. With a drop checker containing 0.5 dKH water I can measure how much CO2 I have in the 1 to 15 ppm range, with usable accuracy. I now have around 5-7 ppm of CO2 vs about 3 or less ppm with no CO2 being added. This small change has made my plants grow at a much faster rate, fast enough that I am back to weekly pruning, which I had not been doing with a low light tank. So, my plants may now be consuming much more of the nutrients than I expected. I will be revisiting this subject soon.

The effect of so little added CO2 shocked me, so I did a lot more research, and found that, at low light levels, we should get this improvement with very small additions of CO2. See: https://www.plantedtank.net/forums/10...ml#post9476106

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