Flocculants only work when the cloudiness is caused by particles much larger than bacteria are. It can work if you've, for example, stirred up a ton of gunk from the substrate and would prefer it get filtered out rather than settle back and sink into the gravel again. In that case, stir it up just enough to keep it from settling and try a flocculant and it may well remove most of it. Flocculants are used as part of water treatment in most water treatment plants on a vast scale.
But for bacterial clouds, they're of little to no help. Usually the cause is an overabundance of organics in the water. This can be from too much crud in the substrate, such as poop, food, dead plants, even dead critters or simply ammonia or nitrite. The organics feed the heterotrophic bacteria which exist in every tank. These bacteria can reproduce at what seems like lightning speed compared to the speed at which our BB reproduce. And so long as the organic load is there, the bacteria will feed on it and the cloudiness will remain or come back quickly after a water change.
A bloom of heterotrophs can actually produce ammonia and in extreme cases cause a spike so watch the water tests. They can also use up too much of the oxygen in the water and suffocate fish, so providing extra aeration is a good idea. Either add an airstone or drop water levels to let water from the filter output fall in, making a good splash, or both. Either will increase gas exchange at the water surface, which increases oxygen replacement in the water.
It's more commonly seen in newly set up tanks than in established ones. I figured out the problem in mine is the food I've been feeding the snails, in an effort to increase egg laying. It becomes a fine powder by the time it hits bottom and too much has sunk into the substrate. It goes too deep for the big snails to get at, and there's too much for the MTS population to take care of. I'm pretty sure it happened because I knocked over a rock while doing a water change, and that stirred up a huge cloud of crud that was trapped under the rock. So I will be doing multiple gravel vacs, water changes and filter cleanings until the water clears. Once I've rinsed most of the organic load out of the gravel, it should clear up.
I'd have to go look up what you do when it's in a new tank.
And I did.. this is a good article on the problem;
http://www.fishforums.net/index.php?/topic/246850-bacterial-blooms-explained/
Chances are you may not have to do much of anything, in new tanks the bloom is often self limiting, once it uses up the organics it goes away. Water changes don't help much, as you can't do enough of them to keep up with the reproductive rate of the bacteria.
In my case the WCS are the unavoidable side result of thoroughly vacuuming all the gravel. I'm actually sucking out sections of gravel so I can rinse them really well, then replace it in the tank. Section by section I'll get it all rinsed out.
Extra filter rinsings will help prevent excess organics I stir up while vacuuming from staying in the filter media. With any luck in a week or ten days, maybe less, I'll have clear water again. I'm going to get a plate to feed the snails on, to try and stop this particular food, which they adore, from sinking into the gravel, but I will also have to do more gravel maintenance to make sure it won't happen again.
Hope yours clears up nice and quick !
