75 gallons is a very popular aquarium. With this volume, the hobbyist can keep many different species and more of them as well. In fact, 60-70% of the cichlid species available to the hobbyist can be housed in 75 gallons. And as far as New World species are concerned, you will find your probability of stocking success is much greater than it might be with a 55-gallon aquarium. Listed below are several stocking recommendations for 75-gallon aquariums, some popular and others quite unique. These recommendations come to you courtesy of the Cichlid-Forum moderating staff.
As already mentioned, the stocking combinations are many and varied. It is therefore unreasonable to comment on every possible setup, even on just those within this article. Individual setups should be researched in order to understand what will work best for your selection. Items to investigate are water parameters, substrate, plants, rocks, and the diet of your fishes. Despite having said this, it behooves us to comment on a few setups.
In general, Tropheus and Lake Malawi Mbuna require lots of rocks. Nooks, crannies, and anything that can function as a cave is highly appreciated. These are readily claimed as hiding, sleeping, and breeding spots. Because of their aggressive nature, caves offer protection and rest to subordinate fishes. Some of the more popular rocks used include: lace rock, shale, slate, lava, petrified wood, tufa, pagoda, granite, and of course honeycomb limestone (aka holey rock).
The Purple & Yellow Mbuna Setup is great for beginners and makes a great show tank with lots of activity. To really bring out the colors, we recommend a blue light (actinic bulb), a black backdrop, black sand (e.g., Tahitian Moon sand), and dark or black rocks (e.g., lace rock).
The West African Setup could be arranged with a couple of different rocky, caved areas with the rest of the aquarium containing large driftwood and being very heavily planted.
The East African Riverine Setup should be very well planted.
The Cave-Dweller Tanganyikan Setup is a little more challenging and should consist primarily of rocks with at least a dozen caves. Each of these species prefers caves to the open water and without these harmony will be difficult to achieve. We also recommend a dark, sandy substrate with an actinic bulb.
75-gallon aquariums should be outfitted with a 250-watt heater to ensure a stable water temperature. Lighting is rather straightforward. A single 48-inch fluorescent light strip is the most common method. For planted tanks, consider using a second strip light. A little more expensive, but justifiably so is the 110-watt Power Compact.
Filter options are numerous. Keep in mind that the total water volume should be cycled through your filter(s) 4-8 times and hour. In other words, to adequately filter a 75-gallon aquarium your filter(s) should cycle a total of 300-600 gallons/hr. There are many ways to accomplish this. Some of the more popular filters are Hang-On-Tank (HOT) filters and canister filters. HOT filters include: Aquaclear 500, Emperor 400, Penguin Bio-Wheel 330, System 1 Pressure Filter, and Cascade 300. Popular canister filters include Eheim 2260, 2215, 2217, 2026; Fluval 404; Magnum 350; Filstar XP3. To really maximize filtration, many keen hobbyists will use a canister/HOT filter combo.
Wet/Dry filtration using a sump is a very effective method that requires little maintenance. Sumps are less popular however due to the higher price and additional work required to set them up. Sumps require a pump, either submersible or external. For specific product information and member reviews of these and other products please visit the Product Reviews Section.
75 gallons is large enough that one could also install Under-Gravel Jets (UGJ). UGJ are appealing for many reasons. First of all, they're cheap and highly customizable. Furthermore, they increase water movement at the bottom of the tank, elminate the need for vacuuming the substrate, and supplement other means of filtration. 
