First off I want to say thank you to Sandnuka as he is the main person that takes care of my account on here as I rarely have the time. So to clear a few things up about discus. First off when considering how to house them you need to realize the difference between doing it as a hobby verses doing it as a business/farm/breeder. Yes I will put 50-60 discus in a 55 gallon as addictedtofish said. The pH he is a little off on, our pH settings: spawning 5.2-5.6, free swimming 5.6-6.0, 1"-2" 6.0-6.5 and 2.5"+ 6.5-7.4. Now water changes, we do 90%+ on all discus tanks daily, the water that we use to replace the water we've taken out is pretreated RO/DI water taken from reserves. It is an exact match to what they are swimming in hence they do not even noticed their water prams change outside of the fact that it is cleaner as we feed them 5-8 times a day. When you do these daily water changes in this manner you are not really relying on your tanks bio system to maintain it. The fact is we have found that the heavy water changes, feeding and how we house them produce healthier discus that grow to full size. Now most all that I have learned about discus came from three very reputable breeders out of Malaysia, Thailand and Sweden. I do not know all there is to know about discus but I have been working with them for 11 years. So would I put 10-12 discus in a 37 gallon tank, yes if they are all less than 4”. Just keep in mind that the water will need to be changed regularly. The daily water changes at 90% is a big factor in how the grow, look at someone who doesn’t do this and you will find that their discus fry are barely dime to nickel size at one month verses our method that have them at 1-1.2” at one month and 2” by two months. You will read online and in books that you need 5+ gallons per discus, if they are full grown yes if not then chances are that you will have much slower growing discus that will not reach their full size.