I'm making an organism which generates its own magnetic field - specifically, a magnetic field which pulses on and off repeatedly. Said organism uses said magnetic field to communicate with other such organisms; why it does so isn't within the scope of this question.
This magnetic field is generated by an organ within said organism. Said organ is made of hundreds of sub-organs. Each of those sub-organs is made of three separate parts.
The first part is a saline-filled tube approximately 1.5 meters long. Its length is relevant later.
The third part is the rather awesome-sounding medullary command nucleus. It's a cluster of nerve cells which controls the function of electrocytes. Medullary command nuclei are another body part unique to electric fish - at least, in real life. Each stack of electrocytes has 1 such medullary command nucleus attached to it.
Each medullary command nucleus is receptive to a single type of neurotransmitter - the chemicals which make synapses function. While the medullary command nuclei in electric fish use acetylcholine as its trigger neurotransmitter, each of these medullary command nuclei uses a different one. For instance, one sub-organ will have a dopamine-activated medullary command nucleus, one sub-organ will have a histamine-activated medullary command nucleus, one sub-organ will have a serotonin-activated medullary command nucleus, and so on and so forth.
Whenever one of these medullary command nuclei are set off by their corresponding neurotransmitter, they tell the electrocyte they're attached to to zap the saline tube that said electrocyte is also attached to. When electrified, the saline tube creates a magnetic field, since running electricity through a conductor creates a magnetic field. In other words, the saline tube is an electromagnet.
The medullary command nuclei shut off soon after activating. Then, they're reactivated by another neurotransmitter. Then, they shut off again. Then, they're reactivated. This repeats ad infinitum. This means that the tube of saline is magnetic, and then not magnetic, and then magnetic, and then not magnetic again, ad infinitum. It is essentially a very weak (I'm going for a strength of approximately 30 microtesla, rather than 100 tesla) pulsed field magnet.
Each medullary command nucleus tells its electrocytes to send out pulses at a different frequency. Dopamine might be represented by a 1-hertz pulse, serotonin by a 2-hertz pulse, and so on and so forth. This means that different magnetic frequencies represent different neurotransmitters.
This is intended to be an inter-individual, built-in communications device. I'm still working on the "receive" mechanism, but that's not within the scope of this question.
See below for a visual representation of one of these saline-tube structures.
Now, imagine hundreds of these elements bundled together; that's ultimately what the organ I'm making looks like. See below for a rough idea of what I mean:
The question: I want each of the (remember: 1.5 meters long) saline tubes in this organ to create a 30-microtesla magnetic field at a range of 10 meters from the tube. What are the optimum dimensions of each saline tube for minimizing power usage, and how much power needs to be run through them to get the current I want?