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JDM 03-08-2013 01:56 PM

Small scale planted tank
1 Attachment(s)
Here is a shot of my tossed together plant only tank.... really just a pitcher that I tossed some leftover sand and duckweed into. Today I dropped in a dwarf pennywort, sprig of red ludwigia and regular pennywort stem with a tiny leaf on it. This is more a little test setup, unheated and using only natural light. So far no fertilization.

I will be periodically testing the water but it starts out today at a pH of 8.4, due mainly to the lack of CO2 in the sun I expect. I'll test the hardness later. I probably could stand to remove some, or most, of the duckweed as it's pretty think in there.


beaslbob 03-09-2013 09:07 AM

As usual looks like you're off and running.

JDM 03-09-2013 09:17 AM


JDM 03-09-2013 10:55 AM

Source water:


plant only jug after two weeks

Not related but tested: ammonia and nitrites zero... No surprise there. I didn't test nitrates, didn't want to have to shake the bottle.

It would appear that my previous conclusion from my aquarium water changes were close to what actually happened. I saw a rough 25% decrease in both GH and KH with plants in the tank and minimal fish. Once I added larger quantities of fish the change in hardness was not nearly so drastic. I attributed the initial change, after some thought and an incorrect conclusion, to the plants utilizing the carbon from the calcium carbonate that makes up the alkalinity (KH). Once the fish were added in greater numbers, the plants then used the easier to obtain carbon from the increased levels of CO2 produced by the fish.

The result in my tank is a sustained harder water with a stronger pH buffer but a lower pH due perhaps to a high fish load and higher resulting sustained CO2 levels. Typically I had a pH in the high 7's and every once in a while, 8.0. Now it is nearer 7.4 to 7.6 pH. I anticipate that as the plants grow out or I add more, that the pH may rise as their carbon consumption capacity increases faster than the fish growth produces it.

So the plant only jug has an 8ppm reduction in GH and an 11ppm in KH (57%). I almost would have expected the absolute reduction to have been closer between the two. I'm not going to theorize why they are what they are relative to each other though... it's lunch time.


JDM 03-13-2013 02:08 PM

dKH is now 8.
Didn't test GH.
pH is hovering around 8.4 still.

There is some dead plant material building up as the thick cover of duckweed finally starts to thin itself out. I'm thinking that the decomposition will bump the ammonia and, while there would be a cycle occur, it will not be typical and I probably won't see any spikes as a result. Given my extremely low nitrate buildup in my aquarium (have yet to cross 5ppm) I might expect to see none here.

I dosed a bit of flourish comp today after testing the water. Curiosity more than anything.

This weekend I may remove 75% of the duckweed... maybe more as I would leave just enough to cover the surface of the water. Debating whether to do that or let the weed figure out it's own equilibrium. The dead material will just form a mulm on the bottom and add to the ammonia source which wouldn't be a bad thing.

Also debating whether to change water or just top it off. If I wanted to have plants thrive in there I would change the water but I am curious to see how soft the water gets and if the pH can maintain it's fairly high level.

I think that duckweed would make a great addition to a planted sump filtration system. I wanted to do that from the beginning but didn't know what I didn't know at the start.


MoneyMitch 03-13-2013 03:28 PM

interesting experiment you have going here, if i were you to keep in the spirit of things, i would let the duckweed figure itself out. worse thing that could happen liek u said is a moonia spike in a planted ":aquarium" not really a bad thing with no fish in there. definately going to follow this one you have grabbed my intrest

Fishnerd101 03-14-2013 07:33 PM

I'd just not mess with the duckweed. Like you said, it'll eventually fix itself and this just and experiment. No harm from an ammonia spike.

JDM 03-16-2013 01:43 PM

1 Attachment(s)
I added some plants today, major trimming in the main tank so I put some java moss , dwarf hygrophila stemlets and a java fern rhizome with a baby attached. I noticed that the regular hygrophila that was already in there isn't doing too bad.

KH is down to 7. Interesting how it is slowing down... of course I now see that had I been actually intending to do an experiment properly I would have tested daily from the start and maybe stuck with just the duckweed.

Anyway, the first two weeks averaged a KH reduction of 0.79dKH per day. Now it is around 0.25 to 0.3 per day. If I were measuring the plants I could track the growth against the KH drop and gain some insight into.... something.... oh, I added top off water twice now, that may affect the KH reading a little bit. With this small a container just doing the testing removes a noticeable amount of water.

I expect the reduction is the slowing down of the plant growth. I'm not sure how the decaying material will affect the growth and uptake of KH. With the pH still pegging 8.4, I doubt that there is much free CO2 in there so I might anticipate the plants to not be doing well soon. The duckweed doesn't show any signs of a major die off though, even though it is as thick as it is.

Here's a shot, lots of disorganized green. Hard to do much scaping with so much duckweed covering everything.


MoneyMitch 03-17-2013 11:35 AM

good theroy with the kh you have there, any plans with co2 issue?

JDM 03-17-2013 12:14 PM


Originally Posted by MoneyMitch (Post 1471815)
good theroy with the kh you have there, any plans with co2 issue?

CO2 issue? There's no issue there. Seeing as the CO2 acts primarily as a source of carbon, the plants get this from the KH component. When the lab tested my water CaCO3 was the primary constituent and I am certain that this is an alternate source of carbon. The slowing down may also be from the other constituents of the KH not being utilized by the plants so there is likely to be some baseline that it will not go below. Seeing as I start from a 20dKH, my baseline might be higher than someone with a 10.

I saw this play out in my main tank as the KH lowered by over 25% while there were very few fish. As I increased the fish load, thereby increasing the CO2 production, the plants continued to do well, at least as well, but the KH has not continued to fall... at least not nearly so dramatically as it stabilizes at a higher value with more fish present. I don't think that the plants are doing any better with higher CO2 than with higher KH.

I'm thinking about trying some solutions of hyper hardened water to add to the jug. Either evaporating my already hard water to increase the concentration while keeping the same contents which might serve to increase the GH more than the KH over time (TDS issue arises here) or just crush up some egg shells to provide a purer source of CaCO3... either that or play with some antacid remedies, I expect they would have other crap in them though. Eggshells would be easier and quicker than a limestone method, which could be an option.

I still wonder about the reasoning behind the CO2 injection. I am trying to stay ahead of plants that are threatening to grow out of my Aquarium (not this little jug). If I upped the light, nutrients and added CO2 I would just need to garden far more often and my expenses and time expenditure would be greater. I know there are many plants that do better with higher CO2 as their carbon source, and obviously plant only tanks would be high in the list of those that could benefit from it, but if the only reason is to provide more carbon in a useable form for the plants in the water itself, wouldn't a soluble substance that can be just added to the water occasionally be easier than having to monitor bubbles and adjusting regulators?

Having said that, I don't agree with the liquid additives with their inherent preservatives.


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