one question: is your pygo tank for life? i mean, will those 8 pygos stay in a 75 gal for years?
because even do that tank is marvelous, really i mean, it looks real great, but it's WAY too small for 8, especially since you have some caribes. caribes will get up to 12" (up to 14 but not in a overcrowed tank) and i guess your tank is not deeper than 16 3/8"...man you will loose some fish for sure, especially that the whole aquascaping(which, again, looks awsome) takes a lot of space.
general rule is calculate 20 gal per natt and 30 per caribes, otherwise, territorial issues will cause death upon your nice (and i guess kinda expensive) shoal.also, lack of space will, on the long term, affect their growth and you'll probably end up with some ugly features such as curved back spine, eyes not on the same height, etc.
technically, you would need a 190-200 gal... when you reach a certain lenght (72-80", this rule becomes less and less essential since the fish have swimming space. so your fish would need a 150 to 180 gal man...
Now, you do what you want, and i know it's not everyone who can purchase such monster tanks, but its just to give you an idea of how overcrowd your tank will be in 2 years (adult size)! i bet a 20 that you don't have 8 pygo in that tank in a year from now.
it would be so sad to loose such great fish, and you reallly have a nice set up man, but it's sad that it's that much overcrowed...maybe you could put 3 of those natts in the 46 gal... not the best, but would last longer than keeping 8 in 75...
sincerely hope your thing will last, but felt i should let you know my thoughts
aight peace man