White scum/film after water changes?

  • #1
Hey all, this has been really bugging me. It seems that about 60% of the time that I do a water change, a white film appears all over my aquarium class a few hours later. I lightly vacuum the gravel, and then replace the water with conditioned tap water. When I went to the LFS they said it was a bacteria and I bought melafix. But now I have a bamboo shrimp and have heard antibiotics can easily kill invertebrates, so I'm worried to use the melafix (plus I don't know if it even helped that much). I tried to get a picture, but the scum is so fine it wouldn't show up, one might not even notice from a distance. It is slimy to the touch and makes the tank appear as if you were looking at it through a very slightly unfocused camera. My snails, ottos and SAE's seem to help take it off even the rainbow shark sometimes goes for it, but nevertheless this film stays on the glass for at least a few days, even if I scrub most of it off. I don't think any of my fish have died from the scum, but for their safety and well-being I'm turning to y'all to help me solve this aqua-enigma. After research I've seen it may be just a precursor to algae, bacteria, or even just calcium deposits because I didn't let the conditioner sit in the water long enough. But at this point I'm at a loss

  • #2
It could be the start of a bacterial bloom, a algae bloom, decaying matter in the tank, oily foods. All of which can be corrected by doing frequent water changes and regular cleanings. Excessive light can also cause the oily slick.

I had a Mystery snail that had been in one place...unmoved for 6 or 7 days. The water was starting to look funky, even though I cleaned the filter and the tank. The water parameters were all in line. My Betta started looking lethargic which concerned me. I removed the snail..problem solved. I believe he was starting to go...slowly. I left him and another one from another tank and put them into a glass bowl. No movement for another 5 days. The scum is gone! This may NOT be your situation, but it's worth checking on.

  • #3
Surface Scum:

This is a build up of skin oils and fish food oils. Adding an air stone/pump to create more surface agitation will resolve this issue. If you can aI'm the out flow of your filter toward the surface this will also help, assuming you have other filtration besides hang on back style.

Another option is a surface skimmer:

In the link above scroll down to #2.

  • #4
To me, the odd thing is that this scum appears immediately after doing a water change. One would think, if it was a bacterial bloom, it'd happen just the opposite, being suppressed when a water change was made, and growing back slowly after that.

Therefore, it must be related to the new water or some procedure done during the water changes.

And the fact that it appears so rapidly also makes me question whether it can be bacteria. It'd have to decide to come on strong, all at once, triggered by the new water, and that sounds pretty far-fetched to me.

One thing that is often seen in tap water is that immediately after you dispense it from the faucet, millions of very tiny bubbles will appear. This is because you've released the pressure that the water was under while in the distribution system. That's a lot like opening the top of a bottle of pop or other carbonated beverage. Releasing the pressure causes dissolved gasses to come out of solution, forming bubbles. But with tap water, the bubbles are usually extremely tiny.

It would be interesting to see if what's happening is that these tiny bubbles of formerly dissolved gasses end up attaching to the glass right after the introduction of the new water.

Close examination should show if it's millions of tiny bubbles. You may need magnification to see them, though.

Also, you could put your tap water in a bucket with the conditioner for 24 hours or so, ideally with an airstone to stir things well, and maybe a heater to prepare the water to be at the right temperature, and then use that "preconditioned" water from the bucket to do the water change. That would allow plenty of time for the dissolved gasses to come to equilibrium with the atmosphere before you put it into the aquarium. This would just be a diagnostic thing. If you find that it's just gas bubbles, then you really wouldn't need to do anything about it.

Does your tap water ever look "milky" right after you dispense it into a glass? I get that, usually when the weather is cold outside. The water can hold a lot more dissolved gas when it's cold, and then, when it comes into the house, it warms up, and cannot hold as much dissolved gas. So then, when I dispense some tap water, the pressure is released, and the dissolved gas comes out, making the water look milky. But I can tell that it's tiny bubbles because the glass will clear slowly starting at the bottom and working upwards as the bubbles move up through the water.

The thing is, though, if this "scum" stays on the aquarium sides for a long time (many days), then that seems to argue against it being tiny bubbles. But they would have a slimy feel to them. That's just a mechanical thing that you do feel when rubbing over a glass surface coated with tiny bubbles.

What happens if you wipe this slime off of the inside of the tank after a few hours? Does it come back?

Do you have good stirring in your tank, and good agitation and movement of the water surface? (I'm wondering about gas exchange at the surface).

I suppose the scum could also come from the disturbance of the gravel during vacuuming, although I've never seen this happen myself.

I'm just kind of amazed that it appears so quickly after a water change. That really makes it seem like something in the new water or something stirred up from the bottom of the tank.

Ninja'd by Aquarist.
  • #5
I'm just wondering if you do a thorough gravel clean when you do your W/Cs? I am thinking along the lines of uncleaned gravel perhaps being disturbed by a W/C, and the film resulting from displacement of the normal bacteria that cause decay being dispersed throughout the tank. Why such bacteria would settle on a food poor spot like glass is beyond me, however. Also, is this a new, or long standing problem?
Glad to hear that you disregarded the LFS's suggesting a med for what is now more an annoyance then a real problem; I like to think of meds like the one you mention as something to be used to a specific purpose rather than something given because they can't think of anything else. I mean, you did say that the inhabitants of your tank are behaving normally, right?
If this is a recent problem, perhaps you could contact your water utility and see if they have changed anything recently, or if you tested your source water when first setting up the tank in order to get a baseline, you might check it again for any differences.
Sorry for a post full of questions rather than suggestions, but maybe a bit more info might help someone here in coming up with just what is going on. BTW, any alterations to your plumbing recently?
Good luck, rick
  • Thread Starter
  • #6
This has been going on on-and-off for about a year now, and my tank has been running for about 3 years now. I have a HOB as well as a canister filter (which I have aimed the outake at the surface), so with all that surface agitation I can't think it would be biofilm. Also, I do vacuum the gravel, but only lightly as to not break the roots of my crypts. I will check this morning to see if the film is still there


  • #7
Can you get a pic of it?
  • Thread Starter
  • #8
Well now most of it is gone, maybe my ottos and SAEs went to town on it during the night. The little bit that's left is not showing up in a picture though
  • #9
That's good to hear......

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