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jhays79 01-13-2013 02:25 PM

Dirt losing the majority of it's nutrients after a year?
I have three dirt tanks setup, and currently I'm putting together a 46 gallon bowfront I plan on dirting as well. I picked up a new bag of MGOPM yesterday, and noticed it says right on the bag "feeds plants continously for six months. Well, what happens after that period of time? Or even a year? I know Diana Walstad doesnt believe the dirt needs replenishing for many years, but I'm beginning to think otherwise. What are the thoughts on this? Do we need to subsidize the nutrients after awhile to sustain the plants? Use root tabs?

danielt 01-13-2013 03:19 PM

Diana also said to feed the fish plenty. Several times she mentioned to feed excessively.

Also, dirt provides micro not macro unless you get some anaerobic action in there. If you keep lightning low it will provide for many years. Otherwise, heavy root feeders will deplete the soil in several months.

Depending on the soil's composition there is a slight possibility for the soil to bind nutrients from decomposing organic matter.

jhays79 01-13-2013 04:48 PM

Yeah, I know she's a proponent of heavy feeding. I have screened a lot of the larger twigs, and wood pieces out of my dirt previously, but now I'm considering leaving them in, to help prolong the effective-ness of the dirt.

Rich Guano 01-13-2013 04:52 PM

What have you been using as a Top Cap over the potting mix? Diana talks about not using anything with a small particle size, because it prevents the return of nutrients from decaying organics to fall back down through the top cap.

+1 on the overfeeding. Fish food has everything a plant needs, but it must be allowed to fall into the substrate.

jhays79 01-13-2013 05:17 PM

I use average size aquarium gravel, not too small.

Rich Guano 01-13-2013 07:13 PM

Perhaps it something other than nutrients. What sort of problem are you running into?

jhays79 01-13-2013 07:16 PM

I never stated I have any problems, I actually think i have my tanks pretty well balanced. I just think it's interesting, and possible that the dirt we use may be void of any nutrients after a short period of time. I re-read the MGOPM bag, and it actually says provides plants with enough food for 2 MONTHS, not six like I originally thought. I'm skeptical that over feeding will subsidize the dirt enough to be effective.

Rich Guano 01-13-2013 07:26 PM

If you can't believe everything you read in a book, then you must also discount everything you read on a bag.

Beer 01-13-2013 07:44 PM

I'm sure the bag also states that you should fertilize with miracle grow fertilizer every couple of weeks. It all depends on how much the plants feed through their roots (for our application) and what the demand is.
Low light, no CO2 = slow growth: nutrients will last longer.
High light, lots of CO2 = fast growth: nutrients will be used up faster.
I'm sure dosing the water column lengthens the amount of time that nutrients remain in the substrate unless you dose lightly and have plants that rapidly draw in the nutrients through their leaves so that other plants are relying more on the substrate, or if you have a ton of plants that only feed through their roots.
How long have your other tanks been set up? Are you seeing any deficiencies (assuming that the bulb isn't old and starting to weaken and shift light spectrum and intensity)?

danielt 01-13-2013 07:47 PM

I don't use any dirt in any of my tanks. Mainly because I started off with teachings of how to maintain a high-tech tank. I don't use any form of substrate enrichment. Although my Blyxa screams at me for some.

You CAN keep almost any plant with water column fertilizers and you can replenish the substrate with clay marbles and tabs.

Monster Fish 01-13-2013 09:57 PM

Overfeeding will not do much for your tank except causing a spike in ammonia.

Dirt will keep on feeding your plants for more than a year or so depending on the nutrient demands of your plants and how much light you place over your tank. As pieces of organic matter in your organic potting soil (such as sticks and bark) break down, they eventually become macro fertilizers for your tank. Look for wkndracer's threads on dirt tanks. All of his dirt tanks have grown plants steadily for more than a year without supplemental fertilization.

wkndracer 01-14-2013 12:12 AM

wrong bag of dirt by what you posted.
I believe MGOPM has ferts added.

Miracle Gro Organic Choice Potting Mix is the bagged product I use.

MGOCPM (potting mix) contains soil and a large portion of organic material (55-65% by volume). Sphagnum peat moss, composted bark fines, leaves, twigs, wood chips etc. and "pasteurized poultry litter" (cooked chicken crap).

Several tanks going with the oldest >3yrs wet.

plantbrain 01-14-2013 02:59 AM

Nitrogen is the only nutrient I think that will not last for many years. Bacteria oxidize it to NH4=>NO2=> NO3 if the plants do not get it. So after awhile, not much is left.

But with a slow rate of non CO2 plant tank growth, and with fish waste, the N needs are typically met.

You can add a little KNO3 once every 1-2 weeks, say 2-4ppm worth of NO3, will not hurt.

I measured a few sediments over time and they all pretty much drop to near zero for NO3/NH4. NO3 does not bind to CEC, which is why many places have NO3 in their ground water.

hecto33 01-16-2013 03:42 AM

i've had a MG soil tank for a little over a year,i capped it with aout 2 inches of sand and i grow an hc carpet with ease

GraphicGr8s 01-16-2013 04:04 AM

What you are forgetting is they are assuming you are using the product as intended. In a pot. Where the soil drys out and you then water it. And some of that water runs out the bottom of the pot. Along with nutrients. I've got a top soil tank running for almost two years. It's never been fed. Most of the time the water level is about halfway until I get around to filling it again. (The downside to that is the mineral content is increased by only adding water. Minerals don't evaporate) Plants are still overgrowing the tank. Without ferts.

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