NO3 seems best at 5-10ppm but this is a bit more flexible "range". You may only want to add weekly or perhaps everyday a little bit each time. Some may have 20ppm at the beginning of the week after adding some to come to about 2 PPM at the end of the week. Some may want to keep a narrow day to day level of 10ppm(+ or - 2ppm) by adding and testing. I've had higher levels than this but the plants I doubt need the higher levels unless you are using 5watts+ per gallon or more etc. I've had some tanks in the 50-75ppm range before with little to any algae but also had lots of light and CO2 etc. I also did 50% water changes so things didn't keep building up but were removed after a week or so with no harm done. How much each tank "eats" should be tested first then a program can be implemented with less testing and a good idea of the tank's needs. I have found that dosing 3x a week with KNO3 and performing 50% weekly water changes allows great NO3 level control and is a very easy routine. One dose after a water change and then once or twice more before the next water 50% change. The large weekly water changes prevent any build up and re set the nutrient levels in the tank allowing the plants to grow at their optimum levels.
Lately, I have been going back to the old methods and just overfeeding my fish to add more Nitrogen instead of adding KNO3. Plants do prefer some NH4+ ion to that of the NO3 but NH4+ is quite toxic to fish. NH4+ is also a great way to induce many forms of algae. I have done a number of experiments dosing NH4+ and adding small fish till I start exceeding the amount of NH4+ the plants can take in. Algae are the result 100% of the time. Performing the same experiment with NO3 does not produce the same result. Adding a larger filter reduces the impact of NH4+ also. Since plants cannot exist with much NH4+ present without algae and/or dead or sick fish they can use the NO3. I have had about 5ppm of NO3 removed from the water column with a well-run plant tank. If plants are stunted and receive not enough nitrogen (either NO3 or NH4+) they will have greatly reduce nutrient uptake of PO4, K+ and most other nutrients but this also includes slowed NH4+ uptake if the plants have been NH4+ starved. Adding NO3 will help the plants use and assimilate the NH4+ faster also.
Fe (iron) can be used from a few different sources. Iron filings in the substrate, fractured clay gravel, laterite, etc can be added in. The water column can have about 0.2-0.5 PPM, although some other aquarist’s water and my own, have been higher than this without issues. Mine was 2.0 PPM at the SFBAAPS (San Francisco Bay Area Aquatic Plant Society) Nov open house for instance. I keep some tanks lower on purpose (0.2ppm or less to zero for no more than two days at a time at moderate to high light) but these have substrate based iron sources so the plants can still have an iron source. These tend to be lower lighting tanks also that get less attention. These tanks are less dependent on a steady supply in the water column and more forgiving. Plants can do fine for up to three weeks without iron in the column so it can be used as an alga control/limiting nutrient (only with a few species of algae) as can N and other elements. But it always gets back to how you balance your tank. Iron test kits have not proven very reliable in measuring actual bio available iron in the water column. But there is a very useful "trick" to figure out the optimum trace dosage for your tank and getting to this point really an ideal path to growing plants well.
By getting all the other nutrients (NPK and GH/KH, CO2) and lighting correct, simply add increasing increments of trace elements and maintain each increment for 2-3 weeks to assess the plant growth. When adding more trace elements has no effect on plant growth/health, that is your target amount. My range at very high lighting is about 5mls per 80 liters of tank dosed 3x a week with either Flourish/Flourish iron (4:1 ratio) or TMG. Sera also had good results. It is unlikely that anyone would need more than this. Dosages of 2 to 3x the recommended amounts are common in a well-planted CO2 enriched tank.

The general trace element fertilizers that are sold have the other elements in there also but iron is the big one to measure. Basing the others off of this reading of iron seems to work fine for the other elements in the mixture for most all tanks. If you are having algae problems back off the Trace element fertilizers and do a water change and add the GH and KH and the KNO3. I think adding more trace element fertilizer if you have a handle on your algae problem is a wise move, even doubling to tripling the recommended amounts in a **well** running tank. This kind of tank would have high light and more CO2 added. Remember: balance is key. If you add more lighting, expect that you will need more CO2 and nutrients as well.
In Marin County, California there's a high level of PO4 in our tap water. 1.1ppm or so and I do large water changes typically, around 50 to 70% weekly. I really don't need to add it in my water. My PO4 levels fall quite fast later in the week. We tested about .5-. 6 PPM after 3 days afterwards a 50% water change with good feedings and OK growth rates. I repeated this test several times afterwards for some conformation. Some folks add it by feeding with fish food (which contains some) but this is converted to NH4, which is the real culprit for causing algae blooms.
I add PO4 by using KH2PO4 since my present tap water is very low in PO4. Other sources such as enemas and H3PO4 (30%) have sodium phosphate and are suitable for adding PO4.The small amount being dosed relative to the PO4 needed have no effect from the acid or the sodium. I have gone up to 2.0ppm of PO4 and never had any signs of algal presence. Having enough present for the plant's needs is all one needs to do. It can be 0.5ppm or it can be 1.0ppm. for your target. Some folks only add enough to raise it 0.2ppm and let it drop to zero or so for a day or two before adding more. These folks are timid and have been told that PO4 causes algae. This is true in lakes where there are no plants. In warmer lake where the plant mass is 30-50% only the plants flourish when PO4 is added to a limited system. Aquatic Plants also need more PO4 relative to N than algae. When plants are limited by PO4 they slow their NO#/NH4 uptake down by 50 to 90 % depending on the severity of PO4 limitation. Adding a small amount of PO4 3x a week will increase the NO3 uptake from 0.5ppm to 1.0ppm a day up to 3-5ppm a day of NO3 uptake. Visually you can see the effects of adding PO4 to a PO4 limited tank in about 40 minutes. If you add some in the middle of the day or at the beginning, observing your tank a few minutes before the lights go off will tell you if the plants are happy and growing well. This effect is quite dramatic and perhaps unlike any other single nutrient.
Potassium (K+) is a wonderfully easy nutrient to dose that helps a planted tank use up the NO3/NH4 and the PO4. Adding it is easy and the target range is quite large. There have never been any reports of over dosing that I am aware of using K2SO4, although some have had some issues with KCl and certain fish and shrimps but this is due to the Cl anion perhaps. I add 1/4 teaspoon per 80 liters after a water change only. I also am adding K from the KNO3 which I add 1/4 teaspoon 3x a week. This will give you the range of about 20-30ppm or so of K. Any build up is removed by the weekly water changes.




Recommended Doses:
Dose Target: Note:
pH 6.5 to 7.0 Lower with CO2 gas only.

KH 3-6 degrees Add Baking soda or premade Alkaline buffer to raise.

Nitrate (NO3) Add KNO3 (Potassium nitrate) a.k.a. stump remover. Fish load and feedings.
GH 2-8 degrees Add pre-made buffers to raise. Or CaCO3 for both KH and GH.
CaCl2 and MgSO4 also.
Iron (Fe) 0.2ppm to 0.7ppm+
Add a good trace element fertilizer*

Phosphate (PO4) 0.2ppm to 0.5ppm Add K2PO4 or fish food or sometimes in the tap water already.
Potassium(K+) 20-30ppm Add K2SO4,KCl and/or KNO3 to boost if you also need NO3. Also in pre-made fertilizers.


If any thing is over these recommend levels do a water change to lower it.

Recommended Levels:
Temperature: 20-30C and a target of 25 C
Water flow: 3 to 5 times per hour (little to no surface movement) or less
Fish load: Light to moderate/algae eaters should be added. Snails are good for this (pond(Physa), Malaysian Trumpet snails(MTS’s or needle points-Melanoides tuberculatus), Ramshorn(Phalnobarius corneus), Amano shrimps(C. japonica), Otto cats(otocinculus sp) etc
Lighting: FL, MH or PC's. Powercompacts, Fluorescent, Metal halide. (Unless your tank is extremely deep or shallow.)

If something is causing you problems in your tank and you test -or not- you can always do a water change then build up these levels to the proper ranges and you should not have problems as long as you keep up on things. Testing helps you from shooting in the dark. It's worth the money and time to test. You'll pay for it if you don't, lord knows I have. So have many others. It's good to learn from experience as long as it's not your own!

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