Why do a blackout to kill cyanobacteria if it's immediately reintroduced to the tank again anyway

I've had severe BGA issues. I can manually remove it all (as in I can't see any left) and a few days later it's back all over the tank. I've considered the often repeated advice of a 3 day blackout, but what I don't understand is how this helps. If you remove it all manually (which is quite easy to do) isn't this the same as what a blackout would achieve? The blackout would kill off all the BGA, but then it would be immediately reintroduced to the tank ( as it's so common). Is a blackout only useful when you have something like a dutch tank where the BGA is impossible to manually remove?

 

I probably would have used antibiotics by now but that requires a prescription. And if cyanobacteria is everywhere, how can you get rid of it forever? My understanding is that even with antibiotics you would only remove your current infestation but the tank would very quickly be reinfected. If BGA is always dormant in the tank, what's the benefit of killing it completely with antibiotics?


Please be patient with me, I can't get my head around this.

 

My nitrates are above 5ppm now, I am dosing EI. But they were zero when the BGA first appeared, I think due to using two bags of purigin.

 

When you say you have to keep dosing, you mean doing a full dose of antibiotics? So you would dose for maybe five days or something like that?


I believe Tom Barr said you will always have BGA in your tank, and that he has it in all his tanks. That's why I'm confused regarding the benefits of antibiotics compared to manual removal or a blackout and then changing the conditions that allow BGA to flourish.


Many have said that once they used antibiotics the BGA never returns. So is BGA as common as people say?

 

I'm currently dosing the API Erythromycin. I'm doing it full strength for the recommended period on the package. It says 8 days. I'm on day three and I think it's working. I'm not very comfortable flushing water with antibiotics down the toilet but not sure if dumping it in the backyard is any better, maybe it is?

 

I did look at chemiclean. I couldn't find out what chemiclean was made of or how it works so I decided not to use it.

 

Hi Julia,


I agree with what you're saying, and that's why I fought the bga for over a month. I completely manually removed it twice a week. I made adjustments to my nutrient dosing. I shortened the photo period to 5 hours. I increased flow and added a skimmer. I increased oxygen at night. I only turned to the antibiotics because I'm out of ideas. Each time I made a change I gave it a week to see if there was a decrease in growth of the BGA, but it never even slowed it down.


The weird thing is I'm was getting good growth under the bga. The stem plants shoot up to the surface so fast I feel I'm constantly trimming them. One set of leaves gets covered in bga so a new set shoots out above. My monte Carlo carpet would literally break through the bga to get light if I didn't clean the bga off for a few days.


It was an imbalance that caused the outbreak. But once it's taken over it seems impossible to recover buy manually removing it. It's all gone now after a full dose of antibiotics, so will be interesting to see if it comes back.