What do you guys think of the initial setup on this new 125 gallon amazon tank?

Lighting is x6 96 watt power compact dual bulbs of 6700k/10k and x6 led moon lights

Filtration - x2 HOB Penguin 200 Bio-Wheel Filters, x2 sponge filters, and 1 CF500 Canister Filter with built-in UV Sterilizer using sponges and cotton pads inside.

Heating - will be x3 200 watt ViaAqua glass heaters

Substrate - layered substrate - fine sand on bottom inch followed by about an inch of established gravel then a small layer of peat moss followed by out 2 to 3 inches of coarse sand/gravel from Lake Hartwell

Fish - currently using established media in the filters but only populating the tank with a small school of about a dozen serpae tetras and then 4 cory cats until the bacteria can begin colinization throughout the tank to handle angelfish

Plants - Currently java moss, java fern, amazon swords, and floating water sprite.

Currently I am not using any CO2 and would love suggestions on what to use for CO2 in such a large tank. Previously I've used DIY CO2 but for a tank this size I don't feel like having a dozen 2-liter bottles under the tank.

the length of that tank is fantastic...nothing beats a low long tank

the longer the better...your fish will enjoy that tank

Sounds like a great set up! I'd add some valisnaria, which is a natural part of the angel fish habitat.

Pressurized CO2 is much less hassel than DIY. You might want to consider getting a reactor which is probably the most efficient way of diffusing the CO2.

" I've read that the filter intake is usually the best method for dispersal but I do have a Hagen reactor that I use on my DIY CO2 which I could use for this tank...it's just a massive eyesore."

Why not get multiple cheap $10 CO2 diffusers and then plumb them up with multiple lines off of one CO2 reactor? I bet they'd all bubble. The tiny bubbles are the most effective, anyway. When the pressure's really high the big bubbles that come out of a single diffuser just rise right up to the surface without dissolving much.
Aquarium air line splitters are like $5 on ebay. Picture: http://i.ebayimg.com/t/Air-Control-Valv ... Q~~_12.JPG

Diffusers are inexpensive at aquatic magic. I think they're kinda pretty.
Picture: http://www.aqmagic.com/images/aa67_12.jpg
Link: http://www.aqmagic.com/equipment-diffuser-c-49_83.html

Although personally I can't see the plants needing more than one CO2 diffuser. My 55 gallon tank used to run a 2 liter CO2 reactor with the 'recommended for 55 gallons' diffuser that I linked to up above and my CO2 was always right at the limit of fish toxicity (30 ppm). It's quite an excellent diffuser, very effective at dissolving its CO2. You could probably get a big dissolved CO2 concentration out of it even in a tank three times the size of my 55. For that reason I'd start out with just a T splitter, like so http://t0.gstatic.com/images?q=tbn:ANd9 ... T4xhVe6ylA run off of one 2 liter reactor. Then check your ppm of CO2. If it's less than 15 ppm, you could go with the 5 splitter and see how that increases it. Or use a 5 liter bottle. But like I said I bet one or two diffusers would be plenty.

Really, CO2 is sort of overrated (except for plants that aren't truly aquatic, which yes, won't live underwater without it). I have half a dozen plant species in my aquarium and I don't run CO2 and everything goes smoothly. Nitrate never rises to above 20 ppm even with me not doing a water change for a few months, which I feel like means the plants are growing fast enough to eat all of the nitrogen from the water column and prevent it from accumulating. Adding CO2 wouldn't be necessary for my aquarium because dissolved nitrogen is probably the limiting growth factor. I doubt adding CO2 would even increase their growth. Also, when I tried that (running a tank with ammonia, nitrite, and nitrate all 0 ppm), some species of plants crashed from lack of food. My <20 ppm (the lowest my test kit reads) is actually sort of dangerous for the plants. I should throw in some rotting meat. Then the CO2 would help them grow. lol, ew.

I'm very much considering going the pressurized co2 route with say a 5 or 10 lb canister. In the meantime I've moved just a single 2-liter size DIY co2 system into place to try to combat the hair algea that has begun taking over. I'll also be adding about 30 dwarf sag to the tank in the next few days. I'm hoping that the plants will begin to outcompete the algea for nutrients.