Ever heard of a plenum? - Page 2 - Substrates - Aquatic Plant Central

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Old 07-11-2020, 11:27 AM   #11 (permalink)
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Default Re: Ever heard of a plenum?

Forgot to make a control for this experiment where there is no plenum and I expect it to go anaerobic. Will use the same material and substrate depth.
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Old 07-12-2020, 09:42 AM   #12 (permalink)
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Default Re: Ever heard of a plenum?

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Originally Posted by chuckm View Post
i have two tanks, a 65 and a 6 (fluval edge) with plenums under a deep substrate of a mix of oil-dri (baked clay absorbent) and eco complete (about 3:1). The 65 gallon has a 3" bed with a 1" plenum and the edge has a 1.5" with a .75" plenum. These tanks are 2 years old, moderately stocked with fish, snails, shrimp and plants. Both have hobs.



My thoughts on the process came from reading up on jaubert, novak and the video series from jay's aquarium which i highly recommend for a plain explanation of the anoxic denitrification process, which is the whole point. From a reef perspective (which i'm not), i also drew on the garf group who advocated a more open plenum system meaning more water circulating. The freshwater systems i'm experimenting with only have access via migration through the substrate and separating mesh.



In retrospect i'm not sure a plenum is needed, maybe only the deep substrate but i'm a believer in anoxic conditions for denitrification. My nitrate levels run around 20-30 ppm which i find very acceptable. I don't do a lot of water changes, maybe 40% once a month or so, and i don't do a lot of gravel vacuuming as a lot of waste breaks down naturally and is absorbed into the substrate. I'm on a well and use that water from the faucet. It's by then passed through a whirlpool household water softener and a ge whole house filter.
My plants and animals are thriving and healthy.
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Old 07-16-2020, 08:19 AM   #13 (permalink)
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Default Re: Ever heard of a plenum?

*15 day update*
I saw little bubbles in the soil, looks like fermented beer or dough. There is a small hint of sulfur, nothing major. I don't know if this is possible but there is a small hint of alcohol as well.
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Old 07-16-2020, 10:06 AM   #14 (permalink)
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Default Re: Ever heard of a plenum?

My take on the whole plenum concept -
It takes up space, the potential downside is way larger than the benefit it might provide (until a sulfur pocket nukes your livestock).

The main benefit is supposed to be that you get lower nitrates.
There's an easier, safer way to do this...
Just run a really, really long (like 10m or more) piece of airline tubing from your aquarium into a nice dark, dark, completely sealed from light, darkroom quality kind of dark box, where coils and coils of tubing sit in total darkness.
Then you hook the other end to a low flow rate peristaltic pump that draws from the tank. If you do it right - right flow, right tubing length, darkness, you will eventually have anaerobic NO3 fixing bacteria in the box of tubing. There's no mulm to convert to H2S, it just lowers your nitrate. If it goes too low (<20 or 30ppm), you either shorten your amount of tubing in the box a little or increase the flow rate of the pump a little.
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Old 07-16-2020, 11:04 AM   #15 (permalink)
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Default Re: Ever heard of a plenum?

There is no reason to concentrate at all on keeping nitrates low. Many people have demonstrated that 80ppm and even higher does not harm their fish. In fact, people who use high light and CO2 also dose nitrates, because they are the first nutrient to run low in that situation. Plants use nitrates, and a well planted tank cannot experience too much nitrates. We used to worry all the time about too much phosphates, but now, for some reason, we worry about nitrates. Growing plants use up both of those nutrients.

I'm just blowing off steam!
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Old 07-18-2020, 07:49 AM   #16 (permalink)
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Default Re: Ever heard of a plenum?

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Originally Posted by hoppycalif View Post
There is no reason to concentrate at all on keeping nitrates low. Many people have demonstrated that 80ppm and even higher does not harm their fish...
A few years back, my reading indicated that having some nitrates was no problem but having either too much (hundreds of ppm) or too little (<40ish) could be detrimental.
Frankly, I'd rather have live plants than the contraption I mentioned above. If, however, you're a keeper of fish that won't allow plants to prosper, a "denitrator" may be worth considering if nitrate buildup is what dictates your water change schedule. At least, that was the thinking the last time I was anything near "current" on such things.
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Old 07-21-2020, 11:02 AM   #17 (permalink)
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Default Re: Ever heard of a plenum?

*20 day update*
Fermentation smell is down, very little sulfur smell.

No smells in the control, 10 days in.
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Old 08-10-2020, 07:42 AM   #18 (permalink)
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Default Re: Ever heard of a plenum?

hmm. My control isn't going anoxic. I'm going to have to add sulfates into the experiments. I have some MgSo4.
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Old 08-10-2020, 08:43 AM   #19 (permalink)
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Default Re: Ever heard of a plenum?

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Originally Posted by mistergreen View Post
hmm. My control isn't going anoxic. I'm going to have to add sulfates into the experiments. I have some MgSo4.

How are you seeing that it's not become anoxic?
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Old 08-10-2020, 09:30 AM   #20 (permalink)
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Default Re: Ever heard of a plenum?

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How are you seeing that it's not become anoxic?
Using the best instrument to detect H2S, the nose.
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