I wouldn't change anything in this tank. Keep the powerhead. You've got a winner.
So, no point in using gravel with larger size then..... Oxygen will flow equally free through 1-2mm gravel as with 5-8mm gravel. The amount of anaerobic pockets are then mainly dependent upon the composition of the soil and off cause the thickness of the gravel layer. So, finding the right balance is then important, you want to keep the soil at the bottom and not in the water layer, but at the same time you want to have as much oxygen in the soil as possible.Gravel size - by itself - has very little to do with creating anaerobic conditions. Anerobic pockets in fish tanks are usually the result of the soil being compacted or weighed down by perhaps too much gravel. A rock, or maybe just the way the soil was packaged before use are other likely contributors. I believe @dwalstad has suggested a relationship between gravel size and healthy root growth in plants.
I have guppies and nerite zebra snails right now, but I will try to add some shrimps too, So, yes, I will keep at least one tank with gravel size of 1-2mm, even though I probably will get a lot of anaerobic pockets after a while. I have already teared the tank down once. I removed 75% of the soil and re-mixed the soil that was left with 50% 1-2mm gravel before I put a 2cm cap on (with 1-2mm gravel). So the bottom layer is now about 3-4 cm deep with 1-1,5cm soil and 2-2,5cm cap. Lack of solid roots systems in the bottom layer will probably ruin the tank after a while. So, it is best to enjoy the tank as much as possible before everything starts to smell againI haven't gone back and read through this thread to see what inhabitants you have in your tank, but if shrimp and MTS are part of the equation then I'd go with the 1-2mm size gravel. Much easier for the MTS to burrow in and the shrimp will have an easier time picking up smaller pieces of gravel as they go about their shrimp business. As JohnWesley has pointed out, rooted plants will help prevent anerobic soil conditions, as will MTS. I'm pretty sure Diana refers many times to the role plant roots play in oxygenating the soil. Regarding the depth of the cap, whatever size gravel you decide on, 1 inch is the maximum recommended. You could use less if you want...its main role is to keep the soil from getting into the water column.
Looks like you was right, after I added some "fresh" iron to the tank my floating plants seem to produce fresh green leaves again.This looks like a classic symptom of iron deficiency--yellowing of the youngest leaves. Iron is the one nutrient that can hold back floating plants that depend on water iron. (Rooted plants can get iron from the soil.) Iron is the one nutrient that is often deficient in the water, because it forms iron oxides and precipitates out making it unavailable to plants and algae.
I purchased FeEDTA powder. I quickly make a fresh stock solution of a pinch (200 mg?) in a cup of water and then add this cup to every 10 gallons of tank water. Doesn't have to be exact. I might add it just once or twice a month.
What a great looking tank! What is the name of your red plant in the background? The plant in the upper right comer, is that "guppy grass"?Plant roots can can keep a soil substrate healthy and not smelly. Unplanted areas should not have a soil underlayer.
In this picture of my tank setup notice how I constructed a front section rimmed with rocks and containing a thin layer of sand with no soil underneath. View attachment 76393
Nice response. Did you use your FeSO4? Or chelated iron?What a great looking tank! What is the name of your red plant in the background? The plant in the upper right comer, is that "guppy grass"?
After I added some "fresh" iron to the tank my floating plants seem to produce fresh green leaves again.
I did try with FeSO4, but it did not seem to work very well. I therefore bought a product called "flourish iron" from Seachem and now it looks like the floaters are happy again. Yes, the red plant you have is beautiful, I will try to see if it is available here in Norway.Nice response. Did you use your FeSO4? Or chelated iron?
Red plant is Rotala macrandra, a gorgeous plant.
I believe that the needle-leaved plant is Star Grass (Heteranthera zosterifolia). It does look like guppy grass.