How deep should the substrate be for plants?

I've heard a number of stories, from one inch on up to several inches.

If I'm using topsoil on the bottom topped with sand/gravel on top, how deep is "deep enough" for the topsoil?

According to Diana Walstad, the topsoil should be 1" and then a 1" layer of medium/fine gravel. She does not recommend sand for the top layer. From what I've read, pea gravel works great.

Sue Kat (a respected Tulsa area Planted tank, Killie Fish, Pleco and Live Bearer breeder) recommends:

The Natural Tank: (Not suggested for beginners)

Low maintenance, no chemical filters. Just use a power head for water movement, with a prefilter for mechanical filtration.

1st layer: Substrate consists of 1 - 1 1/2 inches of an unsterilized top soil or potting soil, with no chemicals added.

2nd layer: 1 - 1 1/2 inches of 2 - 4 mm gravel.

If soil is acidic you can add pelleted dolomite or crushed shells mixed well to gradually raise hardness.

Do not add peat or ferts. You can add decomposed organic matter like compost between the soil and gravel.

From:

http://www.aquatic-o...topic.php?t=316

I have used 3 inches of topsoil with 1 inch of gravel, no problem. In her book, Walstad recommends a much shallower amount due to the potential for anoxic conditions developing. However, all natural aquatic plant systems are anoxic by nature; true aquatic plants have means of dealing with this condition. The only issue is not stirring up the substrate and releasing hydrogen sulfide, but you won't be intentionally stirring it anyway. If you have to remove a huge plant and are concerned, simply treat with peroxide and any hydrogen sulfide released will be oxidized and rendered harmless.

I find that a deeper substrate will last longer. Also, jam some maple or hickory, tulip poplar, or similar leaves in the substrate (just not walnut). The added organic material will slowly decompose and add to your CO2 levels. I have found very nice growth occurs when using leaves.

I very the depth of my substrate from an inch to six inches, though that might be misleading as I have under-gravel caves where the substrate is deep.

One plant was suspended mid-water, neither floating, nor planted and it sent roots down to the gravel and has ten inch roots now. I think if it could, it's roots would keep going down and down and down, so my idea that substrate should be as deep as the plants roots want to go, might not be all that practical. It's cool to watch the fish swim through the roots. (sorry, don't know the name of the plant, it was given to me from someone who got it from someone else who got it from...)

Anyway, currently I have gravel, but I'm planning on going soil. I'm going to let a couple of buckets of dirt to soak for a few months in the hope the algae bloom runs its coarse in the buckets prior to putting the soil in my tanks. I plan to vary the depth when I make the switch.

So, Magnus, it's been almost seven months. How deep did you make your substrate and are you happy with it?

And Nancy, are you against walnut leaves because of the staining quality? Or is there something toxic to fish? I tried a google, but didn't find a correlation. Also, adding peroxide... what ratio?

Thanks!

Walnut leaves contain allelopathic toxins. Who's Nancy?

Walnut leaves contain allelopathic toxins. Who's Nancy?

Obviously, you are since you answered the question. I don't know, I do my best to try to remember folks names and get them right, but I think I'm going to give up the ghost and be like Edward in "Bucket List" and just call people by whatever name I happen to associate with them. Maybe if I pretend I'm rich, they might even let me get away with it!

Haha! Don't worry, you're hardly the only one who's bad with names. I'm not too good with names, either, but at least I'm better than my dad; when I was a kid I got used to being called not only by my brother's name, but by the names of various of Dad's co-workers and even pets.

I don't suppose you have many walnut trees out there in the northwest. If you're ever here in the east, pay attention when you see one; only the hardiest weeds will grow beneath a walnut tree.

I don't suppose you have many walnut trees out there in the northwest. If you're ever here in the east, pay attention when you see one; only the hardiest weeds will grow beneath a walnut tree.

Actually, we have walnut trees that two people can't get their arms about the trunk. I always thought it was the root system/ lack of light getting through that discouraged undergrowth. Live long even I might learn something! It's funny, though when I googled, what I found was the medicinal uses of walnut leaves. Odd that it can be benefiscial to us, but harmful to fish.

Sounds like homeopathic medicine, the central premise of which is that if a substance makes you sick when you are healthy, it will make you healthy when you are sick. I don't know how that one ever caught on...

Walnut leaves contain allelopathic toxins.

This reminds me of something I've been meaning to ask about for awhile. I've seen several posts where people have warned not to use walnut wood/leaves in aquariums. I have assumed it is because of their effect on plants. I know walnut contains a chemical (jugulone or something like that if I remember correctly) that is harmful to many types of plants. Does anyone know if it is also harmful to fish, invertebrates, etc... typical aquarium residents? Also does anyone know if algae growth would be affected by it? I've noticed that there is no lichen on the walnut tree in my yard even though the trunk is always shaded. If it would prevent algae growth and it didn't hurt the inhabitants, I was thinking a piece of walnut driftwood might be a nice addition to a nonplanted tank.

I believe juglone acts as a respiratory inhibitor, which implies that it would affect anything with mitochondria (including animals). However, the only information on its affect on animals I could find was a note that it could provoke allergic reactions in humans and horses.