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Stange oily residue on water surface


Anasfire
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Ok since setting up my tanks at my new place I've notice this strange oily substance on the surface of the water. At first it was only in the 4ft tank and it doens't seem to bother it's inhabitant (Logan - Tiger Oscar) and now that I've begun filling up the 3.4ft its on the water surface in there too. It kind of bunches up into a solid piece if I run a net through it and I can almost scoop it out like pool skimming but some inevitably makes it back to the surface and isn't removed. I thought at first it might be the gravel, it did need a good clean before I moved and I've now put it into the 4ft and 3.4ft where as it was previously only in the 3.4ft but the strange oil has made it's way into the 12L spawn tank now too. It's in every tank that doesn't have a lid bar the tiny 15cm bowl I have 1 female fry in. I had another theory that it was from all the deep frying I've been doing lately but that doesn't make too much sense to me either.. I'm stumped. Can anyone tell me what it is?!

Edited by Fighters4U
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I use a Water Ager CN made by Biotec Restoration P/L in Granville NSW. It did occur to me that it might be the water ager that's causing the problem, eg it might be out of date but I can't seem to find a use by date anywhere on the bottle, so assumed it didn't go bad. I've had it around 6-8 months now. It's super concentrated and the dosage is only 1ml per 38L. I'm in the process of emptying my 3.4ft tank at the moment and going to refil it and see if I get the same residue again. It has gotten better in the 4ft tank, eg not as noticeable but when I run my finger through the water I get an oil, white substance collect in chunks along my finger.

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It sounds like surface scum, which isn't harmful in and of itself. There are a few things that can cause it, but most times it is a build-up of organic matter in the water that collects on the surface. It is basically a thin film of organic matter.

To get rid of it, lay a sheet of butcher's paper or kitchen towel on the surface and then lift it up by a corner. The scum will stick to the paper. Increasing surface agitation should stop it forming to such an extent again.

Some dechlors have a bit of a reputation for bringing this on (stress coat always did it for me), but it can also happen if the fish is shedding slime coat or you underfilter and neglect maintenance.

I use CN and ACN and I haven't had this problem, so check other sources first but don't discount the age thing as who knows what lurks in an 8mo bottle of dechlor :D

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Yeah, Well I think I might replace the bottle of dechlor. I got a big 250ml one to begin with because I thought it would last me longer but didn't count on it lasting this long. At one stage I was using 4ml per day if not more with fry tank WC's etc but haven't had a large amount of fry in quite a while so usage has slowed. I just opened the bottle to see how much was left (it's an solid while bottle) and just noticed is has a funky smell so it may well be off. I did keep it on the window sill of my old kitchen too so I don't think the added heat would have helped matters, probably expedited whatever growth is in there. I haven't been adding it to the tanks any more and the mysterious 'scum' hasn't formed on them so I've decided it's got to be the Water Conditioner and will replace it today. I'll get the same brand as I've found it's great but I'll get a smaller bottle so I use it faster and this problem won't reoccur. Thanks for your replies Mouse and Callatya!

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