They just like to add water to those bags, so they are heavier
. I do not agree or disagree with the eco-complete "bacteria" thing. It is a nutrient rich soil, and I have had good luck with it. I think you would be surprised how long bacteria could survive in those bags. The substrate is mineral rich and the water is heavy black water. There are a lot of organics and minerals for those bacteria. A slight amount of air in the bag. Its impossible to know how long its self life is without knowing exactly what species of bacteria they are using. The heterotrophic bacteria that they claim is in the bag is a very vague term.
I added 100 lbs to my 55gal, I think you will find it too be enough. Its deep enough for my 2ft caecilians to completely burrow in it when they feel like it.
The best way I've found to add eco-complete is to lower the water 30-50%. Remove the lids/hood from the tank. Cut all the way along one end of the bag. Pick it up and add set the whole bag in the tank on its side, then lift up the other end of the bag and the gravel should easily pour out and not make a huge mess. Your tank will still be cloudy for a while.
Your tank is really similar to mine though, same substrate, filter, heater,..ect. Just different lighting.