Wow I can't believe your mega tanks are still running! What sort of major problems have you ran into in the last 10 years?
I love lungifsh, they're the epitome of fishkeeping and I hope to own 1 one day soon. How are you planning to divide the 15000?
Yes lungfish are great.
Problems
I had that problem in 2004 with some fish dying.
I have had leakage around 3 posts (none now as they sealed themselves - could have been caused by a large air diffuser creating large waves in the tank).
I had that leakage beside the one post and the wall but that was fixed and has not leaked since. I had a panel of glass crack in Feb 2012 and that several mfk members patched for me and it does not leak. Not sure what caused it but it happened at feeding time and it could have been caused by the arapaima and the big wallago swimming into each other.
Dividing the 15k
The plan is to use a mesh used by fish farms on an abs frame. All the fish were caught and moved to other tanks or outside ponds by 6 mfk members 2 weeks ago. There were around 180 fish. Since then the steel tie rods inside the tank have had 2 coats Rust Bullet as have the outside posts holding the glass. The steel tie rods will get a coat of liquid rubber next. Also all the rocks in the tank weighing less than 50 pounds were taken out so the tank could be washed down. The tank was then scrubbed and totally clean. I then decided to paint all non glass surfaces with liquid rubber. It will be black when finished which will cause problems viewing the fish at times. However with all lights on I hope it will be OK. The fish will feel more comfortable with the dark background and floor.
I will also be adding 2 1/2" strips of 1/2" glass connecting every panel close to another in the tank.I hope to use the Samona 2 suction cup model with 4 per strip when installing. This should have been done when the tank was built.
I don't intend to add the rocks removed and just use the bigger ones still in the tank. I will also add more larger pieces of bogwood aprox 2x2 feet. I am restricted by the size of the openings above the tank. The big tank has an opening 6 feet by 30 inches so not too many problems in it.
Inspection of the tie rods suggested that one was weak from rust. Since the tie rods hold up the 4x4' and 2x4's holding the light fixures I will install supports inside the tank to hold up the lights and wood so the there will be no problem with them actually falling in the water.
If the divider works and appears it will be OK for the Lungfish I will make another at the opposite end about 7 feet by 6 feet for my aba aba.
This will reduce the main section to 22x10 aprox 9900 gallons
The lungfish will have around 4,000 gallons although I will add some other fish in with him.
The aba will have around 1800 gallons with no other fish put in with him.
The dorado will not be placed back in this tank.