You'll need both of them for adult stage. 17" is a little high but still can do. Only thing I can comment is.... you'll be having REALLY hard time to scrub those fella wall clean. I have 4 units of 2.5' x 5' x 12"depth cement tanks.. got it new from wholeseller at around RM75 each, new... Been using that for 1 year and now changed to fibreglass.... it's like changing from a kancil to a camry... Easy cruise when you do the water change. An idea you can try... line the cement tank with resin. (Ryan, if you are readin this, can you please input some details on those resin+catalyst thing?)

For the tank size... at very very maximum, you can put 7-8 adults. try to have good numbers (minimum 4 fish in any tank cos it will bring you a lotsa benefits)

Maybe you should take 8 instead. 10 will be too much for that tank. But definately temperature will be much more stable than Fibreglass tanks. How much your friend is selling? (if you don't mind publishing the price.. hehe)

But bare in mind, you only need 6 inch water depth. You'll be risking the tail development if you put full tank.

You don't need any filtration of any kind. 100% Water change will do miracles.. hehehe Just a good airpump Regent9000 or equivalent will do the job. Cheap cheap system and very effective. I'd bravely say 99.9% Japanese is doing it this way.

Alternative, You can find all sort of tub/containers with low walls and wide surface area from hardware shop, industrial supply companies, junk yards, etc. Our sensei uses trunk line for trucks/4WD for his ranchus.... see pic; it is a container used by Japanese local construction contracters for cement mixing, it also fit at the back of their truck. Nice....

For fast tracking carpet algea growth.. (just an idea) you can filler the container/tank/tub with 4" of water and get some carpet algea from other tank (but soak it in tap water for a while to kill gems/bacteria) then dump it into the tank together with a few pallet feeds. By the way, no need to dechlorinate the water and give heavy sunlight. If you have planted tank liquid fertilisers... just dump a little in,....

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Japanese Ranchu is another ball game