[mistergreen]

Does that mean that with aerial leaves aquatic plants can produce more O2?

Not sure about that. I doubt it.

If so, where does all that extra O2 go and does any of it wind up in the water column?

O2 will diffuse into the water and any 'extra' will form bubbles that float out of the water (pearling).

 

[dwalstad]

Emergent plants grow faster than submerged plants. They can clean up the water of nutrients (e.g., nitrates, ammonia, toxic metals, etc) faster than submerged plants. But floating plants add no O2 to water. It all goes into air. In fact, their leaves block oxygen diffusion from air into the water, so they can actually decrease the O2 in an ecosystem. That's why you need to have BOTH submerged and emergent plants.

The pond folks know all about this. They always recommend oxygenating plants for ponds (e.g., submerged plants like Anacharis).

Another thing I would say is that my tanks (5,10, and 20 gal) are only 12 inches high. This shallowness helps with oxygenation as there is a large surface area compared to water depth. As tank depth increases, there will be less oxygen entering the system from the air. Oxygen will affect bacterial activity and that can change water purification and many other things.

 

[johnwesley0]

Well, I know it's only been 5 days but I wasn't going to have another chance to measure my parameters for a while. Nevertheless, with only one or two top offs for the past month, my ammonia is still 0 ppm, nitrites 0 ppm and nitrates somewhere between 5 and 10 ppm. Five days ago, the nitrates stood somewhere between 10 and 20 ppm. Normal variation between test samples? Maybe. Put it this way, my parameters rarely improve without a partial water change and I haven't performed one in three weeks. I culled the floaters at the same time that I installed the Safe T Sorb, so it could be either one of them - or both acting in concert. Will check again in about a week.

 

[johnwesley0]

Well, I know it's only been 5 days but I wasn't going to have another chance to measure my parameters for a while. Nevertheless, with only one or two top offs for the past month, my ammonia is still 0 ppm, nitrites 0 ppm and nitrates somewhere between 5 and 10 ppm. Five days ago, the nitrates stood somewhere between 10 and 20 ppm. Normal variation between test samples? Maybe. Put it this way, my parameters rarely improve without a partial water change and I haven't performed one in three weeks. I culled the floaters at the same time that I installed the Safe T Sorb, so it could be either one of them - or both acting in concert. Will check again in about a week.

So...it's been a week and I gotta say...I'm impressed. I just tested my parameters again: 0 ammonia/ammonium, 0 nitrites and this time there's no question, the nitrate level is firmly parked at 5ppm. That's nearly two weeks during which my nitrates have not increased and, to the contrary, have trended in the opposite direction. I have even attempted to "control" for the growth of my floaters:

As you can see, the salvinia minima is corralled behind plastic tubing and has had little room for growth the entire week, normally a recipe for rising nitrates in my bowl. My hypothesis, now a theory, is that denitrifying bacteria have taken up residence in my bowl and the most likely location are the unique surface crags and crevices presented by the STS introduced at the beginning of my observations.

 

[dwalstad]

My hypothesis, now a theory, is that denitrifying bacteria have taken up residence in my bowl and the most likely location are the unique surface crags and crevices presented by the STS introduced at the beginning of my observations.

I think you are right on!

 

[dwalstad]

I was so encouraged by last month's measurements, that I monitored my ten tanks again yesterday. Note that I did not clean or change water in any tanks since the earlier measurements, except Tank # 1 (it got a thorough cleaning, plant pruning, and 50% water change).

The one tank without STS (#9) is definitely accumulating nitrates. Plants continue to do their job of removing nitrites and ammonia without filters, which is what I expected. But the removal of nitrates is totally new.

 

[johnwesley0]

It's been a month since my last water change and for the first time since I began posting on APC, I feel as though I might be able to join the "I only have to top-off" club.

 

[dwalstad]

It's also the Mother Nature club.

I value your input, because it has some thought (e.g., grasp of denitrification) AND you have read my book.

I am very excited about the nitrate results. I have long suspected that in a tank without CO2 injection, plants alone couldn't take up all the nitrogen.

 

[johnwesley0]

It's also the Mother Nature club.

I value your input, because it has some thought (e.g., grasp of denitrification) AND you have read my book.

I am very excited about the nitrate results. I have long suspected that in a tank without CO2 injection, plants alone couldn't take up all the nitrogen.

THANK YOU. And, while I have you...About that #9 tank of yours. Is that a stable 30ppms or do you periodically have to change the water? Just curious.

EDIT: Same question, but phrased slightly differently. Number 9 tank went from 10 ppm nitrates to 30 ppm nitrates in a month's time. Are the plants in that tank able to keep it within that range by themselves or do you have to intervene before things reach a dangerous level?

 

[dwalstad]

Tank #9 was at 10 ppm nitrates a month ago. So it has gone from 10 to 30 ppm in one month. No water changes during this time.

I assume that plant growth and bacterial activity cannot keep up; nitrates will continue to accumulate. This tank is outside where temperatures are now getting cooler and there have been several rainy days without much light. That said, another tank (Tank #8) is outside and it shows low nitrates despite similar conditions. To make a definitive statement I would have to 3 tanks with STS and 3 tanks without, all in the house.

Nitrates alone are not toxic, but if I can, I prefer that they do not accumulate. I am thrilled with results for the other 9 tanks. In the past, my tanks with full substrates usually had 10-40 ppm nitrates.

Today, I cleaned out Tank #9 and did a 70% water change. I am so pleased that I may reset up this tank in the house with STS!

 

[johnwesley0]

I guess this is one of those "the proof is in the pudding" moments:

Now, if that's not 0 nitrates, I don't know what is!
This has been a very interesting last couple of hours because in attempting to answer another question on the "Suitable soils for the Walstad tank" thread, I wound up doing a deep dive on STS only to discover that the stuff has been around for ages. People have always been attracted to its natural, river bed color - and the fact that it is dirt cheap (no pun intended.) It's amusing to read from the benefit of 20/20 hindsight that everyone's initial desire was to use it as a straight substrate. I think because it looked so natural like soil that they had to be disabused of the notion that it contains any nutrients at all. People also wanted to use it as a cap only to discover that it was lighter and airier than gravel and held plants down only with difficulty.

Only one post mentioned STS in connection with the denitrification process and that was only because of its resemblance to Oil Dri, another tractor supply substance that was being touted as the main medium in a so-called, "anoxic filtration system". But, that's a subject for another thread. What's remarkable here is that STS seems to be creating the conditions for anaerobic bacteria to thrive without actually being anaerobic, at least not in ways that are familiar to any of us on APC.
EDIT: familiar to us who work with dirted tanks.
EDIT: Perhaps, it's not a biological process at all, but a chemical one?

 

[dwalstad]

Wow! Talk about confirmation!

I think that you have put two and two together. I agree that STS alone is a poor substrate and as a soil cover okay, but not the best. Oil Dri is in same category as STS--baked clay.

For the potted plant tank, though, STS and Oil Dri might be perfect! They have clay dust and porous crevices for bacterial attachment and colonization. Associated nitrifying bacteria, as they use oxygen, create the MILDLY anaerobic conditions for denitrification even in environments that don't seem anaerobic to us.

Others viewing my results have questioned whether the STS is taking up N directly. I don't think so. First nitrates are negatively charged, so they do not bind to soil particles. Second, plants prefer ammonia, so they aren't going to take up nitrates unless they absolutely have to. I know of no chemical reaction that would convert ammonia to nitrates. I believe what we are witness here is biological process.

Third, any ammonia binding to soil particles is a one-shot process. The NH4+ cation would have to compete with other cations for a limited number of negative binding sites on clay particles (my book, p. 126, Fig VIII-3). In contrast, nitrate respiration is a continuous on-going process. It never stops. Just as we use oxygen for our respiration, these bacteria are continuously drawing down on nitrates for their respiration.

I didn't think a scattering on the glass would make that much difference, but maybe it can.

I cleaned up and brought Tank #9 with 30 ppm nitrates inside where it will have lighting and temperature similar to a "Twin Tank," #7. My concern was that plants in #9 didn't have maximum growth because the lighting and temperature outside were not as favorable as indoors. Attached is picture of two tanks. I tried to make tanks as similar as possible-same water, lighting, fish load, etc. The only big difference is that there is no STS in #9. Starting nitrates for both tanks was zero on 9/12. Stay tuned!

 

[dwalstad]

Preliminary results to report! I've measured no nitrates in Tanks #7 and #9 at 3 weeks. The nitrates that accumulated in Tank #9 while it was outdoors may have resulted from reduced plant growth due to lower temperatures (65F many days) and lower light levels than the indoor tanks. (I've taken PAR readings for shaded sunlight and it is MUCH less than overhead LED or CFL intensity.)

Still, the STS may have had an effect. My preliminary results don't really test it adequately.

Thus, I have ordered some pure KNO3 and NaNO3. What I can do is add enough of the KNO3 to each tank to produce 20 ppm nitrates in each tank. Then, I can monitor the two tanks to see if the STS actually makes any difference in nitrate levels.

Will nitrates go down faster in Tank #7? Will they go down at all? If results look interesting, I might repeat the comparison with NaNO3.

I ordered the two pure chemicals from HomeScience for a total cost of only $17.25. This will provide me with some cheap entertainment over the holidays!

 

[johnwesley0]

This is a wonderful venture on your part, sure to be of interest no matter the results. One technical question, since it's been a while since I've taken a science course: Technically speaking, which tank would be considered the "control"? The one w/o or the one with the STS?

 

[dwalstad]

I don't think it matters here that much. Since I'm testing for the effect of STS, it could be that Tank #7 with the STS is the experimental tank and Tank #9 (without STS) is the control.

Here's some more food for thought:

Planned study with KNO3 additions is to figure out why my tanks don't accumulate nitrates. One possibility is that robust plant growth takes up the ammonia--preferred N source of aquatic plants-- faster than any nitrifying bacteria can convert it to nitrates. So I'm not sure that plants remove nitrates; they just prevent them from being generated in the first place. (In my tanks without filters, this is a possibility.) If I do see nitrate removal, it could be via denitrification. In that case, the STS layer in Tank #7 could make a difference, possibly by encouraging denitrification.

 

[johnwesley0]

One possibility is that robust plant growth takes up the ammonia--preferred N source of aquatic plants-- faster than any nitrifying bacteria can convert it to nitrates.

I wish I had a dollar for every time I've read this: "My NPT has successfully cycled, but I don't understand why my plants don't seem to be growing."

 

[dwalstad]

Reporting unpredicted end of my STS experiment. Presence of STS bottom layer didn't seem to affect 10 ppm added nitrates. But within two days, 4 out of 36 guppies died in Tank #9 without the STS. Emergency! Measured 0.5 ppm ammonia in this tank. Thus, I abruptly ended the experiment by changing 75% of water and adding enough STS (6 cups) to cover bottom of Tank #9. My take: STS not only binds ammonium but provides attachment sites for bacteria that decrease ammonia levels. Thus, while plants purify the water, STS gives me an extra level of protection. Now, I have STS in all of my tanks. None have filters and last week I disconnected all bubbling from air pumps. Photo shows today's picture of Tanks #7 and #9 after stopping the experiment the day before. Water in #9 is a little cloudy due to clay particles, but that's fine. And if you use STS, please do not discriminate against clay cloudiness and rinse STS until the water runs clear. Clay has a HUGE surface area to bind ammonium and provide attachment sites for bacteria. Thus, I only rinse STS once before adding directly to the tank. Clay cloudiness is good!

 

[johnwesley0]

So, what was going on with the spike in ammonia? Does something similar to DAP (p.66 EPA) occur? In that section, you described a reaction whereby certain bacteria convert nitrates into ammonium. I suppose one could imagine a situation where there is an excess of nitrates that triggers a similar reaction that results in higher ammonia?

 

[dwalstad]

It would be impossible to sort out all the variables to make a definitive statement. I doubt the ammonia spike was due to DAP, because DAP is associated with fermentation and very anaerobic sediments.

Time will tell on this one. My goal is to continue to raise and breed guppies in these potted tanks without filters, pumps, and mechanical aeration. Tanks will depend on plant growth with STS as a backup.

 

[johnwesley0]

It would be impossible to sort out all the variables to make a definitive statement. I doubt the ammonia spike was due to DAP, because DAP is associated with fermentation and very anaerobic sediments.

Time will tell on this one. My goal is to continue to raise and breed guppies in these potted tanks without filters, pumps, and mechanical aeration. Tanks will depend on plant growth with STS as a backup.

It was a noble effort. Each one of your guppies deserves a posthumous medal!