[MatPat]

1. My understanding is that Cyanobacteria (which I know is a bacteria, not a true algae) is *everywhere*. In the air we breath etc etc. So, I understand that it's spores are always present in an established aquarium, only blooming and choking a tank should some conditions trigger it (hence my next question). Is this correct for a start?

It looks like you have done your homework Scott

2. What triggers the Cyanobacteria bloom? I've heard that when nitrates bottom out, causing higher plant growth to stop (after all plant tissue stored Nitrogen is used up as well I guess), that this can cause Cyanobacteria to start 'fixing' nitrogen and hence getting a foothold? This would correlate with my findings precisely, my nitrate level did indeed bottom out as I upped my maintenance routine in an attempt to cure a black brush algae problem (another thing to discuss another time).

My experience is pretty much the same as yours, low nitrates or low water flow (or a combination of both) can be a trigger for a BGA bloom.

3. Finally, the obvious, how does one get rid of it? If the extremely low nitrate condition is what triggered it, correcting this would, I guess, prevent it from happening again, but now that the Cyanobacteria has it's foothold, correcting the low nitrate condition, to my mind, won't actually get rid of it? The fact that it is covering the plant leaves will obviously inhibit photosynthesis, so I'm guessing that things just keep getting better and better for the Cyano? My guess is that I need to tip things back in favour for the plants. I have read that either a blackout or anti-biotics will get rid of it - this makes sense to me. I don't see how there could be any other choice with the exception of, theoretically, being able to make the tank larger to accomodate an influx of healthy plants (which can't happen since my tank is already totally occupied with cyano covered plants!). The healthy plants would suck up the nutrients and starve out the cyano. I'm thinking that by using the blackout or antibiotics technique whilst also ensuring that the cyano trigger is removed (i.e. set nitrate to 5-10mg/l), this should do the trick?

Again, you seem to have done your homework. I prefer the blackout method over using erythromycin. Before beginning a blackout, clean as much of the BGA out of the tank as you can. I find it can be easily sucked out of the tank with the siphon during a water change and that is how I usually do it. After the water change add 5-10 ppm of NO3 and completely cover the tank for three days...I've never had to do more than a 3 day blackout. Do another water change after the blackout and add another 5-10 ppm of NO3 and your problem should be solved...as long as you keep the NO3 levels up.

 

[MatPat]

Blackout did the trick. I took the towels away and all the cyanobacteria was gone! I performed a 50% water change and immediately ensured that my nitrate level was set appropriately. I resumed normal lighting and CO2 injection. The plants had, of course, paled a bit, but they should pick back up.

Glad it worked for you. It seems like you have read up on the proper "blackout" procedures and executed them well. The plants will pick back up within a day or so.

I am continuing to measure the nitrate level to make sure that it stays up as the plants start to ramp up again (hopefully).

Make sure you are positive that the results your test kit is giving you are correct. There can be quite a high margin of error on some test kits.

I note that for all the people that have had success with the blackout method there are probably just as many saying that it didn't work.

How could it not work?!?!??? This could only mean that they either didn't block out the light properly or didn't allow long enough (i.e. 3 x 24 hours solid blackout). It could also be that they didn't ensure that the trigger, 0 nitrate level, was removed?

I think there are some people who don not understand that a blackout is more than just turning off your tank lights for a couple of days. Again, you seem to have done your homework and covered the tank with towels and completed a water change both before and after the blackout. You also ensured your NO3 levels were good after the blackout.

I usually tape garbage bags to my tank and add towels, blankets, etc on top of the garbage bags for added light blockage. I always turn my CO2 off and I don't peek to check on the results or to feed the fish...the fish will be fine for 3 days without food. I think a lot of people may forget to do one item or another and not get the same results we have gotten.

I actually blacked the tank out for 4 full days, just to be on the safe side. I know that 3 days is the standard. Has anybody ever had any luck with 2 days?

I've never done a 2 day blackout but it may be worth trying sometime. If it comes back in a week or so you can always do a 3 day blackout. I don't understand why more people don't do blackouts, they are free and that is the best things going for it! That said, blackouts are only effective for Green Water and Blue Green Algae...I have seen people try to use a blackout for nearly every type of algae and run into some serious issues with their plants