17.11.1. Discus Husbandry – Aquarium Science

The “optimum conditions” for DECORATIVE discus are:

Crystal clear bacteria free water created by a lot amount of biofiltration. Cloudy or “dull” water is the enemy of all blackwater fish, including discus. This is the most important variable by far.
Relatively slow moving water which is also well aerated (this can be challenging!).
Adult discus do just fine with any pH from 6.5 to 8.5 and any KH and GH. It is a myth that discus need soft acid water. Another myth is that discus need the conditions they were raised in.
The “optimum” temperature is between 78 and 82°F. (26 to 27°C.) but discus will do well in anything from 75 to 89°F. (24 to 32°C.) with occasional excursions to 70 to 95°F. (21 to 35°C.)
Water changes need to be done ONLY to keep nitrates below 80 ppm. Well meaning “Experts” who make statements like “one must do at least 50% water changes every day with discus” are NOT correct if one has DECORATIVE discus.
Decent quality food with at least 45% animal protein and at least 10% fat by dry weight.
Only peaceful, slow moving tank mates

But note these are “optimums”. Very fine, healthy, attractive DECORATIVE discus can be raised well away from these optimums as long as the water is low in bacteria.

Tankmates for Discus

Discus typically are kept in a species only tank. But some like some other fish in with them. Conventional wisdom is that discus only do well with schools of small tetras like the cardinal tetra. While cardinals may be fine with small juvenile discus, adults discus will enjoy eating small tetras and other small fish. I’ve seen large gourami’s, congo tetras, angelfish, and larger rainbowfish all doing well with discus.

It is often surprising what probably are poor tankmate choices for a discus aquarium You want to avoid anything nippy or willing to chew (some plecoes, some barbs like the tiger barb, many livebearers, some tetras like serpae, rosy and black phantoms). Do you really want a $3 barb chewing on the fins of a $100 discus? Small cichlids like rams or appistos can be a problem as they can get quite territorial when breeding.

But be aware this are not “rules” and many keep discus in community tanks with all sorts of other fish. Just keep in mind that the further you go from the “standard” tankmates the more likely you will have issues with nipping, aggression, etc. If you decide to stray from the standards just be extra cautious and when in doubt move them out, hopefully just to another tank.

Symphysodon aequifasciatus discus — Symphysodon aequifasciatus – Discus

The Planted Tank and Water

Discus love well planted tanks. But this can be a challenge. Plants take carbon dioxide and produce organic compounds such as proteins and carbohydrates. Plant leaves are constantly dying and being renewed. When plant tissue dies it releases dissolved organic compounds. Dissolved organic compounds feed bacteria in the water column.

So getting healthy, crystal clear, bacteria free water in a planted tank is a challenge. Many correctly say that plants “filter the water” and remove ammonia and nitrate. What they miss is that plants add dissolved organic compounds. So plants need MORE, not less filtration, than tanks with no plants.

I find easy plants like vallisneria, java fern or sword to be the best choice with discus. Since I use undergravel filters I put the swords and val in small pots filled with sandy soil. I use a low light low tech type set up.

Many discus owners do not use undergravel filters. They have soil based planted, low tech, low light tanks, with a layer of soil under sand or gravel (“Walstad Aquarium”). Note that expensive purchased aquarium gravels an soils “made especially for planted aquariums” are not options I would recommend. Typically these substrates only work with heavy fertilization, heavy lighting and carbon dioxide additions.

Some beginners try things like adding carbon dioxide injection to a planted discus tank. Be aware that it is VERY COMMON for carbon dioxide injectors to fail and inject too much carbon dioxide. This can easily kill a whole tank of fish. Given the price of discus, high tech carbon dioxide injection is NOT a desirable setup! A low light low tech type aquarium is a much better option. Another good option is a low tech jar CO₂ system. We go over that low tech DIY system in this article:

15.6.1. Low Tech CO₂ System

Discus in the wild cluster tightly in groups of about 500 individuals among the roots and branches of downed trees in the still water in lakes or slow moving rivers. They rarely venture out from these shelters, which makes collecting them somewhat challenging. This is why discus should have vertical shelter like vallisneria, either live or plastic, in their tanks. They love lots of wood and branches in their aquariums. And discus are a very shy fish and like to be in a room which is “peaceful”. They will not do well in a child’s playroom.