Black Phantom Tetras nipping?

Applause for gradually adding fish as water tests allow it. Also well done in putting them in an aquarium that size. You have been doing your homework and then some!

Here are a couple of modest suggestions, most of which you may already the doing:

If this particular source is correct, black phantoms are comfortable between 22 – 28°C / 71.5 – 82.5°F. Fish tend to be more aggressive at the upper end of their comfort range. Try walking the tank's temperature down a degree a day until the tank is at 73 F/23 C.

Sometimes more food will help. Of course then they are digesting more food and you may have to walk up your (often) weekly partial water changes (with treated water of the same temperature, left open over night) to 50%. Some people are appalled at that suggestion & with a long unchanged tank we probably have to walk up water changes 20-30-40-50 % every few days. Nature, especially in the seasons gradually changes 90 % per day with flow from the water table & precipitation. Dirty water contributes to aggression though that doesn't sound too much like what you are up against.

Another possible option, especially with a 30-gallon aquarium is to plant the tank so that there will be several open areas divided by rows or thickets of plants. This may allow males to each have their own territory, while the females cruise other areas.

With a little landscaping, inert rocks can also divide territories. Set the rocks on the tank bottom as opposed to on gravel.

Two great surface plants are hornwort & the broad leaved water sprite. Fast growing & inexpensive Hornwort is great in hard water. Broad leaved water sprite (which can also be planted) thrives in salt free water with a modest mineral level - much like the waters those tetras are from. If either get raggedy do an extra partial water change, check bulb ages & increase the light timer 1-2 hours a day.

Several species of the also inexpensive, fast growing Vallisneria complement the hornwort & can be in groves or planted along the back & sides of the tank. They will continue to grow along the sides, multiplying by runners. As you know, poke a hole in the gravel with your finger, hold the roots in there & dribble gravel around them.

There are several great "bunch plants" in that Hygrophila that make great groves around the tank. There are a number of other great bunch plants. Only buy those that have roots & check on light requirements before buying them.

Fluorescent lights lose strength over time. Replace bulbs over a year old. If you can get a "full spectrum" bulb. A color rating of 5000-6000 K seems most beneficial.

For under the plant canopy there are at least five forms of Java fern. Java moss also is good on the bottom. Just set their rhizomes on the gravel or temporarily attached them to driftwood or rocks with a rubber band or fishing line. (Cut the lines away a month later.)

Bulb plants of the genus Aponogeton are great. Apon. crispus is the first one to get. They may even bloom in your tank! Aponogeton bulbs will usually have a pointed end. Plant the point aiming up. Sometimes they are available in shops as wonder bulbs. If a new batch comes in to a shop, snap a package up and plant them soon. They can dehydrate in the bag.

Ferns of the fern genus Bolbitus can join your tetras. B. heudelotii is a little touchy but can be stunning in a gently running current.

They are a little touchy at first but I also would highly recommend getting a couple of Cryptocorynes or Crypts. The only one that I would recommend for an aquarium set up for less than six months is C. affinis, the prolific Crypt. Because they do not lend themselves to mass production of an emergent (above the water) you stand a better chance of finding them in an independent pet shop or at an aquarium club auction. (Google aquarium club auction and your city, state, province or district. There will be a bunch of auctions this fall.)

Probably too much on plants here. :)

Another long shot when water perimeters have returned to optimum is to add a few more black phantoms. That may spread aggression out more. Because the pecking order is somewhat established, the new black phantom tetras should be the size or a tiny bit larger than those in the tank.

Thinking of pecking orders, it may just be that with a little patience, a little adjusting of the tank, they will settle into a daily routine with less conflict. Good luck & all the best!

Black Phantom Tetra

Ok, you've got a problem. Tetras do better in odd numbers, not even. I know lots of stores sell them in pairs but that's not right.

Even numbers can cause quite a bit of aggressiveness.

You'll need to buy lots of plants for your tetras to hide in.