Recommended acceptable concentrations - The Planted Tank Forum
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post #1 of 5 (permalink) Old 08-10-2016, 09:14 PM Thread Starter
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Recommended acceptable concentrations

1. What are the recommended/acceptable ranges of water concentrations for the following molecular species?
2. By how much and for how long can these values deviate from recommended without hurting fish and/or plants?
3. Do affordable electronic sensors exist to measure each of these?

Nitrogen Cycle:

Plant Nutrients:

Trace Minerals:

Gas Exchange:

Lets assume: a 60G med-heavily planted tank; light 35-40 PAR at substrate; no CO2 infusion; mostly slow growing plants; fish at max - mostly Tetras but possibly also Danios, Guppies and/or Angels - ie: about neutral pH.
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post #2 of 5 (permalink) Old 08-11-2016, 03:46 AM
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For ammonia and nitrite, you will want 0 ppm in an established aquarium.
Nitrates are generally aimed to be 10-20 ppm for good plant growth. Phosphates a few ppm. There aren't really any good potassium test kits out there, so most people don't bother with measuring that.
Iron (and other micronutrients) amounts appears to be contested; I would do more research into this.
Regarding gases such as O2, you want as much as possible. For CO2, it is generally accepted that ~30 ppm is good. You wouldn't want hydrogen sulfide in your aquarium.

Generally, deviations for some less critical species (such as nitrates, phosphates) would be tolerated better than for more critical species (such as oxygen). Of course, a healthy balance must also be struck. You wouldn't want extremely high CO2 levels if you are keeping fish only, but at the same time, without CO2, plants will not do well.

As for electronic sensors, I believe they do exist, but it depends on what your definition of "affordable" is.
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post #3 of 5 (permalink) Old 08-11-2016, 08:19 AM
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See The Lamotte Smart3 Colorimeter cost $898.00. But I could not find the reagent for Nitrate which is a pretty important thing to follow. Another website says that the Nitrate reagent for the LaMotte Colorimeter has been discontinued by the manufacturer. Well that's odd because they have every other reagent under the the sun including the one for cyanide.

The Hach DR 900 multiparameter colorimeter is $1,298.00 at You can get a hundred NitraVer 6 Nitrate powder pillow reagents for $38.79.

Earlier tonight I did a Nitrate test with a standard LaMotte Nitrate test kit. You have to add acid to the sample water then add a powder, invert the tube repeatedly for a minute and then wait ten minutes for the color to develop. Then you have to insert the tube into a comparator and match it against the colors to get a guesstimate. It always helps to get a second opinion on your guesstimate.

Phosphate is harder to measure. I would love to have a colorimeter dedicated to measuring Phosphate. Please post about it if you get one of these sensors. It would be interesting to some of us.

See the Barr Report for dosing Macros. Follow the dosing instructions on the product for dosing micros. Ammonia and Nitrite should be zero. CO2 should be 20 to 30 ppm depending on the light. Dose Phosphate at 10% of your Nitate. Keep your Potassium between 20 to 40 mg/l, in my opinion, beacause I have been having problems with low Potassium. Trace minerals you might not actually have to worry about if they're in your tap water. O2 is critical but usually present.
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post #4 of 5 (permalink) Old 08-11-2016, 04:04 PM
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Nitrogen Cycle:
ammonia - an ion selective electrode exists. However, all ISEs suffer from electrical interference and bacterial fouling, so 24/7 in-tank operation is not recommended.
nitrite - no electronic sensor that I am aware of.

Plant Nutrients:
nitrate - no electronic sensor
phosphate - no electronic sensor
potassium - ISE's are available, but may not reach down to the level needed for freshwater aquaria.

Trace Minerals:
iron - since this exists as both +2 and +3 ions, there are different ISEs for each and they are generally not commercial devices yet. Not useful for aquaria and not low enough detection limits.

Gas Exchange:
O2: commercial sensors exist and are ideal for our purposes, but very expensive.
CO2: commercial sensors exist - also ideal but very expensive
H2S: sensors exist but really not needed for aquaria

Colorimetric methods are more useful for most of the above as Savetheplants noted - I find free phosphate easy to measure colorimetrically. The trick with phosphate is that it can be free or it can be bound up with dissolved organics. Measuring total P is more difficult.


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2g Mac-quarium. Clown gravel, fluorescent plastic plants, and 2 guppies.
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post #5 of 5 (permalink) Old 08-11-2016, 04:46 PM
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What substrate are you using? If you use one with CEC capacity like Aqusoil or Flourite it will affect the water column nutrient levels.

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