I don't have speakers on my pc so can't hear what he says but I am guessing he is American. If he is then typical stupid American thinking using antibiotics to treat a photosynthetic bacteria in an aquarium.
There's enough problems with drug resistant bacteria killing people, animals, birds, fish and reptiles as it is. We don't need to make the problem worse by using antibiotics designed to treat people, to kill things in the fish tank. That just adds to the drug resistance problem we already have.
Blue green algae (Cyanobacter bacteria) can normally be controlled by reducing nutrients, especially dry food, and by keeping the tank clean. If you have major problems with it in tanks, perhaps check your tank maintenance schedule and see if it needs improving. But antibiotics should be the last thing used for this issue.
When one has fish in an aquarium, one has a responsibility to provide the best environment possible, otherwise you should not have fish. Plants are secondary to fish in such a situation. If one wants a tank of "incredible" plants, fine, leave out the fish and then dose the tank with every chemical/antibiotic you can lay yours hands on to improve plant growth and eradicate algae.
It is a well known scientific fact that animals including fish will build up a resistance to an antibiotic. Should the day come when the fish require treatment by such an antibiotic, or a related one, it will be ineffective. That is not responsible fish keeping.
It is also scientific fact that cyanobacteria in an aquarium is caused by high organics in the presence of light. It is easy to correct this by simply restoring/establishing the balance.
COVID has nothing to do with this. Vaccines and antibiotics are very different types of treatment. Vaccines strengthen the immune system to prevent, whereas antibiotics attack and kill.
Let's get a bit realisitic here. When using EM on BGA you need to know two things. The first if you only need one dose to do the job. One does of EM is not going to cause a guild up of resitance to it. However, the job is to eliminate the BGA you have currently. Once it is gone one needs to address the cause as it will likely return if this is not done. Some BGA, when it takes hold, can be difficult to clear.
I had one tank where I had a BGA issue many years ago. I tried everything short of EM and it kept returning. Eventually iIwiped it out for good using my "triple threat" treatment. This is basically for use only the BGA is seriously massive in quantity, it is notfor when you have just a little. The best time to fight BGA off is before it is a serious amount. However, when it gets out of control you do need to knock it down and also to eliminate the potential for it to return.
1. Manually remove as much bga as possible and rinse filter media. Change the filter floss if you use it. Do a big water change.
2. Add only a single dose of EM using the dosing amount one would normally add to a tank were you treating a bacterial infection.
3. Blackout the tank completely for 5 days. Make sure it is well oxygenated. before ending the blackout take a peek into the tank. if the BGA is not all gone, continue the blackout for another 2 days.
At the end of the above be sure to do a big water change and to clean the filter media again.
At the end of this treatment you have decent window to address the nutrient and circulation issues to prevent BGA from returning. Failure to do so can undo the treatment and the goal is not to keep dosing EM over and over. It should be a one time one dose only methodology.