Sparked by a conversation with Wasserpest
, I've decided to perform an experiment to what kind of relationship nutrients and traces have on TDS (total dissolved solids). Bear in mind that ANY/ALL dissolved solids affect TDS. Yet, we only can inexpensively test our water for 5 these dissolved substances (KH, GH, Iron, NO3, PO4). My goal is to see how much
impact the stuff we add to our tanks has on TDS in order to be able to roughly gauge how much "other stuff" is accounting for TDS. In other words, if we know that tank-water TDS is 600, and we can account for 400 of this TDS using tests for our 5 major compents, then we'll know that 200 of that TDS is made from things we don't test for. And, consequently, this can give us better insight as to whether we are overdosing the "untestables" (like trace minerals and potassium) in our tanks.
I yield that this is NOT an exact science. But, it is
a means to gain some insight into the "untestable" aspects of planted aquaria.
Part 1 of this experiment will deal ONLY with individual nutrients and how they affect TDS. In the coming weeks, I will be adding a 2nd part to this experiment involving the long-term testing of TDS on my planted tank, and the impact plant uptake of nutrients has on TDS. Part 1 will set the foundation for part 2.
Oakton meter, capable of measuring 0-1990 TDS.
500 mL bottle
1 mL syringe
Kent Proplant (Iron and K)
Potassium Nitrate (mixed from dry ferts)
Mono Potassium Phosphate (mixed from dry ferts)
I started the experiment by simply pouring some Seachem Flourish into the cap of the container and taking a reading. My TDS tester read "error" because the TDS went over 2000.
So, I realized I'd have to do some dilutions. I added 1 mL of product solution to 500 mL RO water. The RO was tested each time prior to adding any products to ensure that TDS read 0.
After adding 1 mL solution of Flourish, the tester read 50 TDS. Therefore, Seachem Flourish has a TDS of 50 x 500mL = 25000 TDS
I tested the other 2 commercial products
Seachem Iron read 110 TDS for 1/500th concentration = 55000 TDS
Kent Freshwater Proplant read 190 TDS for 1/500th concentration = 95000 TDS
Next, I tested my two nutrient mixes KH2PO4 (mono potassium phosphate) and KNO3 (potassium nitrate). The KH2PO4 was mixed to a concentration that would increase PO4 in my 46g tank 0.2ppm for each mL added. The KNO3 was mixed to a concentration that would increase NO3 in my 46g tank 1.0ppm for each mL added.
KH2PO4 read 70 TDS for 1/500th concentration = 35000 TDS
KNO3 read 420 TDS for 1/500th concentration = 210000 TDS
It may seem to some that because both chemicals contain potassium (K) which we can not test for, this portion of the experiment is riddled with error. But, in truth, it is not, since a TDS meter measures the K as well. So, while it is true that we can not measure the potassium individually, we can account for the total TDS that nutrients add as a whole to our aquaria. In other words, we can account for the things WE add to the aquaia. This applies to all things we add to our aquaria. A TDS meter measures it all.
Is this a vague way of assessing nutrients? ABSOLUTELY. But it does give us some
means to gauge concentrations of traces, potassium, and other untestables.
For reference, my tap water has a TDS of 400 with the following parameters.
The final part of part-1 of this experiment was to test if the sum of the 5 products' TDS added in one solution equalled that of the sum of the individual TDS readings.
Total of individual readings.
Flourish = 50 TDS
Flourish Iron = 110 TDS
Kent Proplant = 190 TDS
KH2PO4 = 70 TDS
KNO3 = 420 TDS
Total = 840
One mL of each added to one 500mL solution = 790 TDS
, giving us an error of about 6%. Close enough to surmise that this error most likely resulted from slight measuring error, and not because of a more complex relationship.
In part 2 of this experiment, I will practically apply these findings to the health and maintenance of the aquarium by monitoring how TDS increases and decreases with nutrient addition and uptake. Specifically, how to subtract
TDS for testabe nutrient uptake in order to better understand the amount of "untestables" that have/have not been absorbed by the plants; giving us some
insight to trace absorbtion.