irridescent shark life span

Question
right now the remaining irr is lying on his/her ( i think female because of larger size) side tail and fins still moving i can pick her up and move her around and she swims for a bit but then lies back down. is there anything else i can do? still eating but not much.
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The text above is a follow-up to ...

-----Question-----
I was wondering what the life span of irr. sharks are in a home tank. I recently had one die after 9 years and now the other is dying (still fighting) i think he/she is lonely but i don't want to bring in another baby. (waiting to afford bigger tank) Both sharks have made several road trips (moving NY to KY, KY to co) and were fine out lived all the rest and i just wondered if there is anything i can do better with the next pair i buy.
-----Answer-----
Hi Kirk;

Wow! Those guys really were experienced travelers! Their life span is about 10 years or more so it sounds like you have been doing a great job caring for them. I don't know what I could tell you to do differently. You have already successfully raised yours and they just become old. It's still sad when they do finally die though. So sorry it's been the 'end of the road' for them.

All I can offer for advice for new ones is since they do have the potential to get over 2 feet long, be sure whatever tank you keep them in is VERY large. I would say no smaller than a 125 gallon, and a 240 or bigger eventually. Lots of water changes too. Big fish are pretty messy without even trying. Replace 25 of the water every week and vacuum the gravel at the same time.

But, then again, who am I to argue with previous success? ;-)

At Your Service;
Chris Robbins

Answer
Hi Kirk;

Poor thing. There is very little you can do really. You could make a partial water change to help the metabolism and immune system. Change no more than 25% of the whole tank and be sure the new water is the same temperature as the old water. Use a water conditioner too. You can do the water changes daily as long as they are 25% or less.

Raising the temperature helps too, but make sure there is plenty of oxygen in the water with an airstone or extra flow at the surface from the filter. The higher the temperature, the lower the oxygen saturation in the water. If you can get the temperature slowly up to about 80 it might help her metabolism.   

You could try feeding brine shrimp. I use frozen because it's easier than trying to keep live and less messy than freeze-dried. It's an "aromatic" food so she may be more enticed to eat it if the other food is less exciting.

Hoping for improvement....

At Your Service;
Chris Robbins