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A 2 inch layer of potting soil under a 1.5 inch layer of gravel. Its in my 55gallon. 4 40 watt flouresent bulbs, 2 20 watt bulbs, 11 hours a day, and soon to be pressurized co2. :arrow:
 

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Sounds good with a couple of caveats.

Make sure your soil mix is well saturated. Paul Krombholz, a long-time champion of soil based substrates on the APD, advises making a "soil soup" out of it first.

Also, make sure the gravel you use is fine enough to contain or cap your soil mix.

I like the idea of a soil based substrate, few trace element/mineral issues and great growth as long as the right dirt is available locally and the un-decomposed organics are held in check.

Unfortunately, I'm too much of a chronic re-arranger.

bobo
 

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testing potting soil

I would test the soil for composition before I used it. Its easy to do. The reason I do it with potting soil is that a lot of potting soils are about 90% mulch (ground up bark and peat moss etc). Tom Barr recommends very little peat be added to non soil mixes (gravel, flourite, etc) so I try to keep the organic matter down to about 10%.

I put a handful of the soil in a soda bottle with water and shake it up. Then put it down to settle for a few hours. The components of the soil wll stratify with the lighter organic stuff like peat floating to the top layer and floating on the water surface.

What I found after a lot of checking was a locally produced "top soil" at a nursery that had only about 10% organic matter. So thats what I used in the tank.

From prior experience I found that this soil gets very muddy when wet. So muddy that I didn't think it would support the top layer of gravel. So by experiment I found that if it was cut 50/50 with the cheapest builder's sand I could find (Sakrete sand at Home depot for $2.50 per 70 pounds), it works out pretty well.

The 50/50 mix also ensures that the soil is not too rich. With this setup the water turns yellowish for a couple of weeks but then is OK (50% water changes weekly). So I don't presoak the soil.

With this setup you have a lifetime of micronutrients in the soil, but still need to provide macros. With your high lighting you will need to provide to the water column KNO3, KH2PO4 for the macros. To be safe I also dose micros using Plantex CSM+B to the water column.

Regards,
Steve Pituch
 
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