How Much Beneficial Bacteria Does Gravel Vacuuming Really Remove?

[GoldenRoses]

Every fish keeper knows that you aren't supposed to vacuum more than half the gravel in your tank at a time. It's supposed to keep your colony of beneficial bacteria in check, as vacuuming all of your gravel at once removes loads of bacteria, stalling or even crashing your cycle... right?

But how much bacteria does vacuuming your gravel reallyremove?

The question arose from the fact that I do massive water changes and gravel vacuuming every week on my goldfish tank. They're such messy fish that 60-80% water changes and 90% gravel siphoning are required to remove the fecal matter and other debris in the tank. I'm doing deep gravel cleanings on almost the entire tank at every water change, which can range from once per week, or even more depending on how much time I have. But despite this fishkeeping sin, I've never had any issues with toxin spikes at all, neither right after a water change nor days later.

I suppose that it could be the fact that I haven't touched the filter elements in over two months, so a strong colony of bacteria (and pond snails) have established in the canister. Maybe, as the goldfish keep growing, I will have issues one day that comes from over siphoning the gravel?

But then again, I can't see how merely siphoning the gravel could remove that much beneficial bacteria, as they stick to the gravel itself. Plus, the goldfish are always foraging through the substrate, picking up and spitting out the gravel, so could they continue to the lack of bacteria aswell? If there even is a lack of bacteria...

Any insight would be much appreciated. 

 

[nic1]

Hi, beneficial bacteria can grow anywhere it can attach itself to. This can also include aquarium walls, decorations, outside of the filter box (if it's internal)and even your fish as well as gravel. Siphoning the gravel is essential as this is where all the waste falls, more waste equals ammonia spikes, higher nitrates etc,
As your gold fish grow, the amount of bacteria will grow to accommodate their waste if that makes sense? It is built up over time so is aclimatising and grows over time. If you was to dump a load more fish in instantly forcing the amount of waste up then that's when you may encounter problems!
Maybe someone can elborate on t his for me, but you kindda get the gist of what I'm saying Ive gotta go do the school run!

 

[the_lock_man]

Every fish keeper knows that you aren't supposed to vacuum more than half the gravel in your tank at a time. It's supposed to keep your colony of beneficial bacteria in check, as vacuuming all of your gravel at once removes loads of bacteria, stalling or even crashing your cycle... right?

 
That's a new one on me.
 
As Nic says, the bacteria live pretty much everywhere, not just the gravel - and in any case, they cling on pretty darn tight, so, IMHO, you lose negligible numbers of bacteria when you vaccuum - and that's backed up by what you've seen in practice.

 

[eaglesaquarium]

As stated above, the opening line is a myth.  First, the beneficial bacteria live on ANY and ALL surfaces that provide them with a place to live and proper water flow (access to nutrients).  Second, the bacteria CLING to these surfaces, so there's no risk of sucking them all up when doing a gravel vac.  Finally, the amount removed/disturbed and placed in a less conducive location to their function may cause a fraction of the colony to die; however, the colony can usually double in around 24 hours, under optimum conditions meaning any losses will quickly be replenished.
 
 
Long story short, gravel vac as much as you wish with no concern of losing a large percentage of your colony.  The issue is not in your husbandry, but the understanding of the initial premise you proposed:
 

Every fish keeper knows that you aren't supposed to vacuum more than half the gravel in your tank at a time. It's supposed to keep your colony of beneficial bacteria in check, as vacuuming all of your gravel at once removes loads of bacteria, stalling or even crashing your cycle... right?

 
That is misinformation.  That may have been a rule years ago, but it has been dispelled.  A great amount of your bacteria lives in your filter, which is where there is a lot of water flow, tons of the nutrients required and its generally dark (the bacteria seem to do far better in darkness than in light).  That should be rinsed monthly, or more frequently in a very dirty tank.  But, again, the bacteria cling to surfaces, so they will stick around after a gentle swooshing.  No worries.

 

[l_l_l]

I never vacuum my gravel but it's for complete different reasons.
I like stuff building up there so my plants eat it. Makes me put less chemicals in my tanks.

 

[Byron]

I agree with others.  It is very difficult to dislodge bacteria from surfaces, and you certainly will not do so by water changes and vacuuming into the substrate.
 
The extent of the substrate cleaning depends upon the aquarium.  As some have noted, plant nutrients come from the breakdown of organics by bacteria primarily in the substrate (this is the main source of CO2 in low-tech or natural planted tanks).  With or without plants, more bacteria live in the substrate than in the filter (in a balanced aquarium with a suitable substrate depth) and there is a complex chain of interactions occurring in the substrate that is essential to a healthy aquarium, so you do not want it "clean" to the point of being pristine.  But when you have fish like goldfish that produce lots of waste, you have to get rid of much of it or it will overload the system.  When there is more organic matter being deposited in the substrate than the various bacteria [and here we are not talking solely about the nitrifying bacteria but many other species] can handle efficiently given the tank size and water volume and substrate depth, other problems will arise.  Higher nitrates, the pH may drop too far, etc.  So continue your cleaning and water changes.
 
Byron.

 

[Gruntle]

As I see it, the main danger in siphoning gravel is stirring the gravel from top to bottom in the substrate. If I correctly remember the wise words of TTA, bacteria will only grow in the top 1/2" of gravel (unless other factors are at play, such as a heavily planted tank).  Siphoning stirs the gravel to new depths, so if your tank is like mine, with around 2" of gravel in the bottom, there's a chance that the gravel with the bacteria clinging to it will end up deeper than 1/2" and the bacteria will not survive/grow/replicate/whatever.
 
But if you have goldfish, your main concern will be waste from the fish, so removing that would be far more beneficial than not siphoning.
 
There's no way to tell exactly where the highest concentration of bacteria is in any particular tank, but evidence suggests the majority should be in your filter (darkness, water flow, nutrients, everything mentioned above), and quite capable of reproducing rapidly enough to replace any (quite likely negligible amount of) bacteria that may get lost by siphoning the substrate.
 
When I kept goldfish, my main water problems were caused by following the manufacturer's advice and replacing the filter cartridges every month (and throwing out all the bacteria that had colonised). Since I found this site, I've had ever so much more control over my tank! And since switching to tropicals, the waste they produce is miniscule, and my plants appear to be taking up nutrients from the waste, so I rarely vacuum any more.

 

[ellena]

I think this is from the days when under gravel filters were used, so all bacteria were in the gravel, there was no other filter media. Though, as has been pointed out, you can't really suck bacteria up, as they form their biofilm.