Well this thread was a fun read....I am glad for once some little retics made it to a home that actually cares. I personally can not believe the cost you paid for these little guys for starters holy moley and I have had guys give me a hard time for selling captive bred retics for $80, that are eating like pigs when they are 4 days old and never stop! Retics are probably the least cared for rays in the hobby, however they are one of my favorites I love their personalities. They were my first rays and I still have my first initial 2. My female is now 14 inches and my male about 10 inches. And so far as of today they have given me 8 wonderful litters of pups. You said your rays are around 6 inches if I read correctly which would probably put them at about 6-8 months old if I had to guess. Definitely need to invest in a "python" water changer it will be the best investment in fish keeping you will make besides your great FX5 you just got. And definitely the sooner on that 180 the better. And just FYI retics due to their long tails can out grow even a 180 I can't imagine my big female retic in a 180 with tail she is 21 inches nose to tail and she is missing almost half her tail. These animals create huge bio loads if you haven't already figured out LOL so the bigger that tank the more water the less chance of all your parameters going crazy.