The problem i have with any kind of carbon dosing such as vodka is that its a bandage for more underlying issues that persist even with dosing.
1) no tank should have a nitrate problem unless overstocked, over fed, or under maintained.
This is what creates the problem.
2) carbon dosing is seen as a fix. Many people ignore maintenance and water changes once they start seeing nitrates disappear
This creates a reliance on carbon dosing. Carbon dosing is a risk. If you overdose have widespread bacteria blooms then you will have an even bigger problem. Carbon fuels ALL bacteria growth not just nitrifying bacteria. That means cyano
Ive seen many people dosing carbon have an outbreak of cyano
and then it only gets worse as you continue to dose. This could put in a position you have to quit dosing before you have a tank over run with cyano
or other bacteria bloom. Since you cant dose your nitrates rocket up and tank crashes. Its a catch .22.
3) many unknowns still. Not everything is yet known about the effects especially long term effects of carbon dosing.
This means long term expect unforeseen problems after all your dumping god knows what into your tank in hopes of cleaning up the mess you started.
Ive seen first handle on multiple occasions when carbon dosing goes bad. Your playing roulette with your fish and your money. This is a completely avoidable problem that many of us give advise so that its avoided. I find that usually people who need to carbon dose go against most general recommendations for some reason or another.