I believe that's E. trigona. It's one of the easy Euphorbia that accept regular soils, but they really perform a lot better with a fast draining mix with lots of inorganic aggregate mixed into a compost- or peat-based soil. Miracle Gro works fine for them. You'll probably want to get something like lava rock, hydroton or coarse perlite to add to the mix for drainage though. Gravel works but is heavy; in smaller pots that can be a good thing, but if your plant grows into a monster and you've got to move a five-gallon pot full of wet media and rocks... well I guess what I'm trying to say is that a big spiny poisonous stick like E. trigona is not the plant you want to be manhandling.
This blog has some helpful cultivation info on this and other Euphorbia.
My understanding is that they're from montane grasslands where there's a cool dry season and a hot rainy season, so they're not really desert succulents - they have the ability to tolerate moist soils and the same warm-climate conditions that most typical houseplants prefer. All Euphorbia descended from grassland plants so they have some ability to tolerate moisture, but they have more adaptations for living without water than they do for living with a lot of it. I imagine that they're the evergreen shrubs in regions of productive seasonal grasses and wildflowers, with a dry winter where everything dies off or is eaten by persistent herbivores. Thus the milky poison sap and nasty little thorns.
E. trigona is from the "Euphorbia" subgenus of Euphorbia, which seems to include a lot of the cactus-like species that still tolerate and even appreciate heavy watering and feeding when you time it right. But even if you can treat them like a houseplant in ideal conditions, they're still succulents, so a well-drained mix that you can let go dry is a good safety precaution.
Aquarium water shouldn't be counted on for complete plant nutrition. People do successfully use fish emulsion - poop vacuumed up from gravel aquarium beds, often in tanks stocked with fish known for having heavy appetites. But it's used with nutritional supplements and consideration for the soil it's being added to, not to mention where it's used 'cuz it stinks to high heaven. Likewise if you just dump aquarium water into a hydroponic system you'll often get a frothing, soupy, reeking mess. Water or emulsion both need to be prepared or a special hydroponic system has to be employed, either consisting of a simple biological filter or otherwise a full-blown ecology of other organisms (
aquaponics) that serves to break down nutrients into forms the plants can use, manage excess nutrients, and keep diseases and pests in check.
Which is not to say you can't do it - actually doing it right is a really valuable lesson in horticulture whether you're building a hydroponic system or just mixing compost. But keep in mind that aquarium water is basically a dilution of algae and poop, and make sure that however you offer it to your plants, it's the plants that are using it. The safest place to use aquarium water is in your garden outside.
~Joe
PS - My 4000th post! Hooray!