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Discussion Starter · #1 ·
Well, I've been waiting since September. Today I received my LaMotte potassium test kit. I can not confirm whether my math was right all this time. :)

Anyone else use a potassium test kit or are we all guesstimating?
 

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Calculation versus Measurement

OK,
But which do you think is more accurate: the expensive test kit, or the calculated amount of pure potassium compound that you put in the tank? I would trust my calculation any day versus what a test kit told me.

That's whole jist of Plantbrain's idea. Don't trust the test kit! Add the nutrients as if the test kit was not telling the whole truth, and then reset the ingredients weekly with a water change.

My Hach TPTZ Fe test kit is supposed to be very good, but it never agrees with what I put in the tank. I think it is better to go with the "empirical" method. Calculate the dose accurately, measure the dose accurately, and just put it in the tank. :) I would use the Fe test kit to check the difference in doses, say, if I went from .2 ppm Fe to 2 ppm Fe, as an experiment, but I would still trust my calculation more.

Just my two cents. Actually I am envious of you having the kit. :wink: I feel your overall experience (and your results) in this hobby far exceed mine. But I would be using the kits for checking orders of magnitude, not a 5.5 ppm vs. 10 ppm difference, which I think is not too meaningful. Unless you doubt the math you used to calculate the dosage. In that case I can calculate it for you.

Stve Pituch
 

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Discussion Starter · #5 ·
Steve,

Thanks. Here is how I use test kits.

Test kits should not be considered to be the determining factor when dosing because they do have a margin for error. This is especially true in colorimetric or turbidity test where it is difficult to tell minor color or turbidity differences that are necessary with minor differences such as .1-.2 or 5.5 and 10 ppm. Therefore, doing the math helps to get your doses within a certain range and why Tom says don't trust the test kits. Of course, if you are using cheap kits, their margin for error is higher and the chances of something blocking their reading is also high. This is another reason why you shouldn't trust the kits.

Having a range of a certain nutrient is what is important. I like to keep my K between 10 -20 ppm for example. Therefore, I just use my math and test kits to make sure I'm within that range. I think most hobbyists should do that.

Fortunately, I use a colorimeter that is able to read the color/turbidity using a computer and laser. This provides a high degree of accuracy. As I'm using LaMotte test kits, I have a high degree of confidence of my readings. Most of the time, I'm more or less on point with the math.

I use math to calculate how much of a certain nutrient I will be putting into my aquarium. For example, how much KNO3 I'm going to dose my tank to get 10 ppm K. I use the test kits to tell me how much my tank is sucking up between water changes. Doing this I found I have to dose every couple of days to stay within range. This is particularly important in high-light, CO2 enriched tanks. How would you do that with math only? I recall Neil Frank once being surprised to find K levels in his tank over 75 ppm! How do you know how much accumulation is taking place without them?

Test kits can be a valuable learning tool especially for beginners. We shouldn't discount them unless we are sure they can result in wrong conclusions.
 

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While you know how much you add to the tank, and know how much you remove at water changes (well...do you truely know the real volume of water in your tank? do you truely know how much you remove from the tank each time. ...and are these numbers more or less accurate than the accuracy of the test kits?) you do not know your plants uptake. Suppose you have a good idea on uptake, do you know if your uptake is stable? are these uptakes etc fall within a narrower margin of accuracy than a test kit?

...just thoughts :)
 

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Art,

It seems you are using the kit the best possible way. Get an initial reading perhaps after a water change and before you add the ferts. Then put a calculated amount of ferts in the tank, wait 30 minutes and then take anther reading and compare it to your calculated amount plus the original residual amount. Then take additional readings at periodic (daily?) intervals to see how the plants are consuming the nutrient. Hopefully the nutrient won't change so it doesn't read the same by the kit.

Start this on the 58 gallon tank please! :lol:

Steve Pituch
 

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Discussion Starter · #8 ·
Steve,

Yes. That's about how I use them. They are only a tool.

I will post exact readings tonight when I get home.

I also use the kits on my experiments. For example, I am testing out the use of akadama as an alternative to Eco-Complete and Flourite. I need to see the impact it has on water parameters- mostly GH/KH.

I therefore calculate an amount of GH/KH I want in the water before putting in the akadama. I confirm with test kit. Then I add akadama and test water periodically thereafter to measure the impact.
 

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K+ test kits did not tell me much in the range I needed when I used them, 20-30ppm.

I suppose if you try to run the K+ down etc for some reason, or add lots etc, it might be of use.

Personally I sold mine.

It works etc, but it's just one of those nutrients I'm not worried about as long as a fair amount is present, dosing KNO3 alone does that for my tanks.

Regards,
Tom Barr
 
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