I am not a shark expert, but I am drawing from my experience in the public aquarium field at an institution with a big shark collection.
We fed the sharks 3-4x per week. I cannot remember specifically what we fed (I recall chopped squid and mackeral), but we also used a proprietary vitamin. Occasionally, the sharks would supplement their diet with a tankmate.
From my experience, nitrates are not much of an issue with sharks. Public aquariums often have high levels (1000+ mg/L range would not be uncommon). I am not kidding. They keep the lighting dim and scrub algae like crazy. A day at the office is spent in SCUBA gear srubbing algae. Imagine having to hold it while you worry if that 8 ft shark thinks that your leg would make a nice appetizer.
Water changes on tanks half a million gallons and larger get really expensive and difficult. Consider the logistics of mixing salt by the pallet. We changed maybe 5% per month. In order to do this you need heavy mechanical filtration, biological filtration, and ozone. I would also invest in a big scum sucking protein skimmer. Something rated for like a 5k tank.
By all means use ozone. Just test your water frequently for residual oxidants using HACH DPD total chlorine test. This test is cheap and colormetric. You do not need a fancy spectrophotometer, just mix the reagents and look at it. Any visible pink color is bad news. I like the 25ml test. Get an ORP meter to help manange the ozone dosage. You do not need some super high efficiency unit. Do not follow the notion that bigger is better. Just enough ozone to get water clear. Do not trouble yourself with disinfection.
If you are using IO or similar salt you need to worry about secondary oxidants from the bromine. I would recommend running the treated water through carbon to prevent problems. Also, good insurance is to run the post ozone contact water through a tower of bioballs to help offgas any ozone.
What are you going to do with the sharks when they outgrow the tank? We kept 4' pacific blacktips in a 10,000 gal tank and it could get pretty exciting in there. I cannot image having them in a smaller tank.
These guys are going to really dirty up the tank. I would be looking at big sand filters for swimming pools. Here big is better. Baker Hydro makes a good 3 ft dia. one. Get a multiport valve also. You pipe the waste on this thing to a drain. When the pressure gauge reads high, you turn off the pump turn the valve to backwash; restart the pump and wait for the water to run fairly clear. With one of these you can clean your mech filter in no time and with little fuss. Of course, the more you backwash the bigger the water change.
Sorry, if I have been a bit long winded. I saw the post and I had to chime in.
Hope this helps.
Jim
