Soil question for the Walstad tank

Thanks. Very helpful information, and the best thing is that you have shown us that it works!

What I like is that this iron product is readily available and does not contain any other stuff--NPK, sulfates, other micronutrients. Note that gluconate is also sold to humans as the calcium supplement 'calcium gluconate', a form of chelated calcium. Thus, it is totally harmless and bacteria would be expected to break down the gluconate as they would DOC. FeEDTA will also work, so pricing and availability would be main determinants for these products.

Here is product information from manufacturer:

"Flourish Iron is a highly concentrated (10,000 mg/L) ferrous iron gluconate supplement. Plants are able to easily derive a benefit from Flourish Iron because ferrous iron gluconate is already in the ferrous form so they do not expend energy reducing it. Despite what other manufacturers may intimate, gluconate is not harmful to plants or fish. In fact, ferrous gluconate is better suited to foliar feeding than is iron-EDTA, owing to the relatively weaker iron-gluconate bonding vs. iron_EDTA bonding. In addition, ferrous gluconate has the added bonus of being a source of carbon."

Last update. my floaters grow slowly, but have a nice green color after Fe supplement. In contrast, my H.polysperma grow like crazy (see pictures).Can the reason for the slow growth of the floaters be explained by lack of ammonium in the tank? Water contain enriched levels of nitrate and no ammonium or nitrite.

So, back to the gravel size. In my current tanks I am using gravel size of 1-2 mm resulting in a lot of debris on top of the gravel cap layer (food, fish poo, plant debris etc). Should I do regular vacuum gravel cleaning or should I just let it be? It is not that easy to vacuum clean the gravel in a jungle planted tank......

I currently looking at different gravel sizes as a cap for a garden soil in small tanks. Gravel sizes 1) 1-2 mm 2) 2-4 mm and 3) 4-9 mm.













Do you think I will be able to measure any discrepancy in water parameters between the "tanks" after some weeks/months?

Thanks for your reply, I will leave the debris alone then. It does not look so great with debris at the bottom, but it is not easy to remove the debris either without seriously disturbing the plants. Yes, I am not sure what is going on either, as mentioned the H.polysperma and N. hydrophylla "Taiwan" grows fast, while the floaters, which grew really fast in the beginning are now growing slowly. Another plant that grows slowly is the Red Tiger Lotus (Nypmhaea Zenkeri), and the red Alternanthera Reineckii seem to slowly die (not grow at all). Further, Hygrophila corymbosa is not growing much either, but it is still there, so it is not dying either.
Would have been nice to be able to measure CO2 levels, but I guess you need expensive tools to do that. I think maybe the floaters grow faster with excess of ammonium and nitrite than nitrate? Do not know if iron affects the growth rates of the floaters or the H.polysperma. Maybe it was fish and fish food that increased the growth of H.polysperma.

Anyone had nerite snails in a tank? They seem to lay white eggs on the tank walls and some kind of white slime/mucus that does not look so good. I will try to take a photo of it.

So, after about 2 weeks after setup we can observe two things by looking at the pictures.

1, Different levels of tannins (organic materials) in the water layer.
2. A water surface membrane can be observed in the bottle that contain the highest amount of tannins

Did a JBL strip test yesterday and it seems like the strip to the far right has a slightly higher pH and GH/KH (from the sample with the largest gravel size 4-9mm).
Will do more water tests during the week.

So, first the good news, my floaters look good in all three tanks. No more yellow/pale floaters, cured by adding iron to the water layer.

Then the bad news, it looks like I have another nutritional plant deficiency in one of the tanks? The question is what do I lack? After testing the water layer with a JBL test kit it seems like the water layer contains enough NO3, PO4, iron and K. Still my H.polysperma is loosing its older leaves and gets nasty spots (see pictures below).

An update from Oslo...
From my testing, I found "sowing soil" to give best plant growth in my tanks. However, when using pure sowing soil with a cap I got quickly an anaerobic bottom layer with a bad smell of sulfide. When I mixed this soil with around 50% natural forest soil the anaerobic problem was minimized. Some of the problem with the other soils may be due to high pH in the soil layer as a water test after about 6 months showed high pH in the water layers of these soils ("Tiger" and "Oslo"), see attachment.

From left to right: "rhododendron", "sowing", "oslo" and "tiger" soil, water (JBL strip test).

So, I will give it another try.
I have been looking for "good soils" where the amount of nutrition is given.
I found this one (see below, "old sowing soil" to the left, and the "new flower soil" to the right.

The "new flower soil" has an organic content of 39,4% and contains peat, cow manure, sand, bark, compost, and calcdomite (nothing more, nothing less). From the list we can read that the "flower soil" contains 131mg/L vs 80m/L of NO3+NH4, 66mg/L of P vs 25mg/L, 440mg/L of K vs 150mg/L, about the same levels of Fe, and pH (6,5). It contains about the half of Ca and Mg (225 vs 110 and 220 vs 120) as the sowing soil and much less S (15 vs 60mg/L). So, less S may be beneficial to avoid sulfide smell? Question, does it matter how much N there are in the soil? Will high levels of N speed up degradation of organic material in the soil?

So, wise from experience, I would like to mix the "flower soil" with something before using it as a bottom layer. They do not sell Safe -T-Sorb here in Norway, another option would be ADA amazonia soil (high CEC capacity) or natural forest soil.

I am also testing various gravel sizes as a cap. These bottles (see below) are a couple of months old and I have now added som floaters to see if I can observe any difference in grow rates. Will also check the water parameters with various water tests next. From the pictures we can see that the amount of tannins from the soil is more evident in the bottle with the largest gravel size. I have not been able to separate the bottles on behalf of production of air bobbles from the bottom layer. All three seem to produce "air bobbles" when the bottom layer is poked. The air bobbles do not smell yet....I have 1 inch sowing soil with 1 inch inert gravel cap in these.