(1) You mention fine gravel as cap over the soil. Could you post pictures to give an idea of grain size of the gravel you mean. Have you ever experimented with different caps and noticed any positive or negative experiences or one working better than another. For instance, pool filter sand, Schultz Aquatic Soil, Soil Master Select, tahitian moon sand vs pea size gravel.
Here's an image comparing the different gravel caps that I've used. I have not used any of the ones you mentioned. For me, as long as the gravel size is paired well with the root size, I'm not too critical about it. I have never gone below a gravel size of 1-2mm in size.
(2) What photoperiod do you run your lights and have you noticed any positive or negative effects on plants or algae with different photoperiods. If so, what photoperiod would you recommend.
Nothing special here... 12 hours. I have not experimented with different intervals.
(3) How long have your tanks been running? Have you noticed and effects of substrate nutrient depletion(via plant nutrient deifciency symptoms) and the need to add more water column ferts over time.
Most of my tanks run for a year or more. Not that they couldn't run longer... I just want to try new things. I did experiment with running a non-co2 tank at about 100 umols/m2/sec of light and it did great for about 10 months without algae - then, all of the sudden at the 10 month mark, it totally went south. All the plants turned pale and algae became dominant. I attributed it to the soil finally giving out - but can't say for sure.
With my current non-co2 tanks with soil substrates, I have been dosing using EI. I dose it the same way as I do my CO2 tanks, just less frequent. It's too early for me to tell how this will extend the life of the soil.
(4) Do you follow the 1 inch per gallon rule of stocking when it comes to fish/snails/shrimp. Do you generously stock your tanks or keep stocking to a minimum? How frequently do you feed your fish?
I keep stocking to a minimum. In general, I prefer relatively few fish, with heavy plants. I feed them only once a day, and sometimes skip a day. I only feed them live or frozen foods. No flake foods.
(5) Finally, what is your water change schedule like and how much(% of total tank water approximately) water do you change?
In my non-co2 tanks, I never change the water. Periodically, I check the nitrate and phosphate levels to modify my EI dosing routine.
On the CO2 tanks I change 50-70% of the water every 1-2 weeks.