I would only use saltwater aquarium rated pumps - surely they are available where you are? That's all I would consider for any of my tanks. Generally, all the metal parts of these pumps are encased in wax and a robust plastic housing. The only parts that touch your water are a plastic impeller mounted on a ceramic magnet. I think it is mounted on a stainless steel shaft, but I've never had a problem with them.
Mind you, copper pipe is the standard plumbing material in the US ever since Columbus, and I've run several octopus tanks with seawater made from good old tapwater and never had a problem.
I have a situation... we have a place right off the sea. We purchased a 250 gal tank and a seawater pump (cast iron) to bring in saltwater directly from the sea into the tank. For this type of situation , is the equipment needed for the setup and maintenance the same? should the seawater be fed into the sump tank then filtered into the main tank as would a smaller reef aquarium? what kind of filters should be used?protein skimmers? Live rock and sand will also be used directly from the seabed. We would like to try rearing and want the conditions as healthy and natural a habitat as possible. What brand names and models are the best to use in this case? We will be journaling the progress and growth of the octos. Also if we start with seawater does the tank have to be cycled for the required three month period before adding the octos? or can the time be shortened if the tests prove appropriate levels?
Are you designing this as an open water system? All the filtration info I have goes out the door if you're using real, mother nature-blessed seawater. If a constant supply of fresh seawater is directed to the tank then there's not really much to do to it otherwise. Be aware that you're at the mercy of whatever is in the ocean near you- my girlfriend was running an open system with her cuttlefish lab in Holland and a weird tide that brought in too much fresh water (or local pollution- they're still not sure) killed everything in the lab.
Designing is exactly where we are stuck!
Problem is keeping that pump going for twenty four hours- electricity cost ! the pump would have to be shut off most of the day leaving perhaps a short time for a fresh supply of seawater.. so we are back to square one! I need help! what would be the safest equipment to use to insure i wont kill everything in the tank one day? How can we put this altogether and run it right?
The best times to switch the pump on and off would be better in regards to the tide rather than to the day/night cycle. But as Jim warned a high tide could bring in all nasty kinds of stuff.
Personally I think it may still be easier (safer?) to use synthetic seawater and perhaps a HUGE sump if it's water volume that you are worried about? A very large tank I have set up as a reef (14feet by 3 feet by 4 feet) has 3 sumps totalling about an extra 2000 gallons in it.
My knowledge of open systems if limited also. But i do know that you wouldnt have to cycle th etank if you had a constant supply of tank water, but a week or two of running may show up any future problems likely. You also will not need skimmers or carbon etc. however, pumps for circulation may still be necessary.
After thinking about this for awhile, I'm with Colin. Where any sealife is concerned, especially invertebrates, stability is just as important as water quality. I've heard many horror stories where hapless aquarist noticed their octopus/coral/fish/whatever getting sick, and changed half the water in their tank- which immediately killed the sick animals. A smaller and more gradual water change might have saved them.
That said, I imagine a difficult scenario to maintain water stability in your tank with an intermittently running pump feeding new seawater. I would opt to use the pump to fill your tank, then let the tank's filtration polish the water- a nice big sump and a W/D system with a skimmer. Fire up that cast iron pump to do your monthly 10% water changes, and that's it.
Whatever the scenario, the only time you're exempt from the 3 month tank cycle waiting period is if you're running a full blown open water system. There's no way to speed it up- the nitrogen compound levels are classically the only thing aquarist worry about when setting up a new tank, but there is a lot more going on in your water than having bacteria break up nitrogenous molecules. A newly cycled tank has just barely caught up, but in that 3 month waiting period, biologicals colonize your gravel, sand, rock and filter, and stability is ensured.