I could be wrong but there is something about this program that bothers me? - Page 2 - PPS Analysis and Feedback

hoppycalif · 06-29-2008, 05:19 PM

I just finished reading an old "Barr Report" from 2005 on the subject of potassium and aquatic plants. The most relevant part I found is:

Quote:

The amount of potassium removed through crop harvests is quite large. Typical concentration of potassium in healthy foliage range from 1 to 4% on a dry matter basis. It is reasonable to assume the same with aquatic plants given their rapid growth rates. In several crops, K removals are much larger than nitrogen and in some cases it is as high as 3 to 4 times that of nitrogen. It is used in larger amounts than any other element except N. Many plants have "luxury consumption", the plants take up more than is needed. K is not a part of any structural component of the plant as it is located in the cell sap as an inorganic salt.

Does this say more potassium is removed through pruning and pulling out plants than you calculated?

hoppycalif · 06-29-2008, 10:13 PM

If I have put 1 mg/L of K in the water per day, I have put 365 mg/L into the water in a year. A 10 gallon tank is 10x3.75=37.5 L of water. So, in a year I will have added 365mg/L x 37.5 L = 13690 mg of K, or 13.7 grams of K.

Per Tom Barr's paper on the subject, dry plant mass is at least 1% K, so to eliminate 13.7 grams of K would mean disposing of 13.7/.01=1370 grams of dry plant matter, or 1370/454=3 pounds of dry plant matter in a year, or less, if the percentage of K in those particular aquatic plants is more than 1%. A healthy aquarium will easily grow that much plant mass in a year, to be pruned away or pulled out and tossed. And, one wouldn't dose that much of any fertilizer unless the plants were growing well in response.

Did I miss a decimal place somewhere?

ray-the-pilot · 06-30-2008, 05:58 AM

3 pounds of “dry waste” is right; however, aquatic plants are about 98% water so if you include the water, you have to throw away:

3 x 100/2 = 150 pounds which is not that far from my estimate of 190 pounds.

Even going with the 4% dry weight that would mean throwing away about 38 pounds in a 10 gallon tank. If you have a 100 gal tank you would have to cart away 7 pounds of waste a week.

Of course all this is speculation. Someone needs to check the K levels over time to see what happens.

Here are some other points about these no removal plans:

What happens to the excess SO4 and Ca? Where do they go? Has anyone checked the change in conductivity of their water over time? This would be an indicator of a problem?

Everything you put in has to come out somehow. If not, you will have a desert!

Edward · 07-01-2008, 05:31 PM

Well, the usual way here is to have people saying such a dose is absolutely not enough. Good to have you here. Ok, the dosed K amount was determined mostly on experiments done with a TDS tester and fully planted aquariums without water change for as long as three years or so. For example dosing more and more K while watching NO3 consumption to level up determines sufficient amount of K. All done on daily basis and maintaining consistent levels for test kit accuracy then calculated long term additions divided to an average per day dose. Additionally, watching TDS long term consistency as a proof of the right dosing levels and ratios.

ray-the-pilot · 07-02-2008, 06:06 PM

Quote:

Originally Posted by Edward

Ok, the dosed K amount was determined mostly on experiments done with a TDS tester and fully planted aquariums without water change for as long as three years or so. For example dosing more and more K while watching NO3 consumption to level up determines sufficient amount of K. All done on daily basis and maintaining consistent levels for test kit accuracy then calculated long term additions divided to an average per day dose. Additionally, watching TDS long term consistency as a proof of the right dosing levels and ratios.

Now that is really good information!

OK, I really don't have a problem with PO4 and NO3 the biology is that they will really go away over time. The problem is with the "spectator ions." The things you need to balance those acid radicals. K and NO3 are not used the same way in plants and checking for NO3 does not say that K is at the same level!

TDS is a clue that you are not overdosing with K but it is not convincing. If your water started at a TDS of 150 ppm and ended at the same value it could mean that there was 150 ppm of calcium and magnesium and now there is 150 ppm of K.

If you are not going to take any water out of your aquarium you have to check everything that you put in it including SO4, Cl, Na, etc. All of these can build up in a way that is independent of anything else you put in your tank.

OK, I think this plan is actually pretty good and I'm doing a modification of it in my own tank. The difference is that I am doing 20 - 30% water changes per week. By doing this I can add the same amount of nutrients that you recommend each week and be absolutely assured that it is impossible to have more than the recommended levels of nutrients in my tank.

I would be really interested to know the level of K, SO4, Na and Cl in a three year old tank with no water replacement.