So back on track to all posters - if this was your tank, what would you add? (please be specific and pick your mostest bestest choice under the conditions given at the beginning)
You can try Heros severus, or some Geophagus sp.
Other big fish like an Arowana, maybe.
In the end your fish will tell you who is living with whom.
Oh but it is a autotroph and not a heterotroph. Just because it is prokaryote and not a eukaryote does not mean it is automatically a consumer and not a producer.
Now with that said - yes antibiotics will work against cyanobacteria - I know, I'm a Pharmer. It is better though, IMHO, not to use antibiotics whenever possible. It waste money, builds up resistance in bacterial populations, kills off good bacteria (i.e. nitrosomas and nitrobacter), and does not get rid of the source of the problem.
Rarely do I use caps in forums - but this is one of those moments:
when treating cyanobacteria, DO NOT USE ANTIBIOTICS!
Cyano is more complex than credit is given. It has the ability to adapt to many environments including light and dark phases and can extract nitrogen from the atmosphere directly. It can survive in extremely low nutrient levels once established and can out compete many plants.
With that said, 400+gallons with a cyano outbreak would require some aggressive maintenance to prevent a serious outbreak. Activated carbon helps if it is of high quality.(low ash/phosphate free)
Water changes will help only if the source water is not the source of the nutrient. Otherwise, fuel to the fire.
Your light intensity and duration will have an affect on it's proliferation. An 8 hour cycle per day would be a stable constant to begin the battle.
Alkalinity/buffer affect cyano also. If water quality is degrading due to an accumulation of DOC's and reducing the pH, then WC's and a buffer may be needed to stabilize the system.
The use of Granulated Ferric Oxides in a reactor is an excellent way to reduce available phosphates(which are apparent). I especially prefer Warner Marine phoSar HC. The HC represents High Capacity. The product works much better and lasts longer than normal GFO's.
Identifying the source of the fuel for this outbreak and limiting it is a priority. Some forms of cyano and dinoflagellates can and do release toxins. Although usually an unsightly, slimy algae it can become a problem for more expensive sensitive fish.
Finally, if the cyano is introduced to a well maintained established system and water changes and carbon are not winning the battle, then the use of Eurthomycin is usually the fastest way to rid the tank of this nuisance. Albeit, too small a dosage will not kill all the bacteria and give it the ability to resist future doses. Still, the use should not be ruled out. Everything in this hobby has it's place. Knowing when and where that place is, is the key to success.
Big tanks are great! But mathematically they can be a bear to recover when water quality is neglected. Meaning lots of extra water changes, media replacements, adding up!
A 36w or higher UV may be a good investment on this system. It would help keep water bourne bacteria at a minimum(nitrifying bacteria grow on surfaces, hence "surface area" being so important), and prevent any green water episodes, not to mention a reduction in DOC's that normally would cause yellowing of the water.
I have kept very large tanks in both frsh and SW. Once you pass the 300g mark water quality issues can creep up and become a problem without a good understanding of the chemistry at hand and a good plan in the event something is wrong.
. The tank should start popping here pretty soon. If you are having problems with the algae though, just add some water sprite, it looks great, it also grows fast, which used up all the nutrients that the cynobacteria needs...
I hear ya on the cheap lighting scenario....there myself at the moment.... 
