Strange film - caused by rust?

[DiscoveryHill]

This is a pond at a school habitat garden. I have drained, cleaned and refilled it, but this film keeps returning. I’m thinking it could be caused by the rust. We have gambusia in the pond and they are staying alive despite it all. The film is slick, rainbowed, and clumps together. Suggestions on what it is? Also, how should we treat the rust? The tank is only a few years old and should not have rusted this badly so soon. Also of note - because we are on an elementary school campus, we can only have 6” of depth, so the majority of the tank is filled with rocks and soil. Thanks!

 

[mrsclem]

It looks like oil. Are you running a pump? Some pumps are oil filled. As far as the rusted tank, could you empty the tank and drop in a liner?

 

[j.w]

@DiscoveryHill
Yep it looks like an oil sheen.

 

[bagsmom]

Interestingly, I have had this rainbow colored film in a container garden with no mechanical stuff whatsoever. I did water changes and it kept returning. Is there a yucky smell? My water smelled horrible and the oily sheen kept returning. In my situation, I believe there were rotting plant materials in there and the whole thing was just out of balance. I ended up just dumping it, which made me sad. But I couldn't fix it, despite my efforts.

 

[Lisak1]

Welcome!

I agree - looks like oil. Could your pump be leaking? What kind of "tank" is this?

It does concern me that you say "the majority of the tank is filled with rocks and soil". Too much substrate can be a big problem in the bottom of any pond.

 

[Lisak1]

@bagsmom - that was my concern exactly with the bottom being filled with rocks and soil. A nasty situation could develop from the build up of debris.

 

[DiscoveryHill]

It looks like oil. Are you running a pump? Some pumps are oil filled. As far as the rusted tank, could you empty the tank and drop in a liner?

There is no pump or anything else that would use oil. We just had a few inches of rain and even after a few days, it’s clear and looking great again. Makes me wonder if there is something in the tap water?

 

[mrsclem]

Doubt that its the tap water. More likely as others have stated, with dirt and rocks in the pond, rotting plant material can give off a bad smell and oily sheen.

 

[DiscoveryHill]

Ok, thank you for all of your help. I misspoke earlier when I wrote that it was filled with rocks and soil. I talked to a colleague who was here when the pond was established and she confirmed that it was filled with river rock only - no soil. That being said, I think you are all on to something about there just being too much substrate in general. The rocks were placed years ago and I think there has been plenty of time for plant matter to build up and throw off the health of the pond. I drained and refilled it recently, but it sounds like I need to empty it out completely and clean out the rocks. Thanks again!

 

[addy1]

A lot of work, but worth it in the end.

 

[Stephen Noble]

I think it is outstanding you have this pond in a school setting. Way to go! There is a clue in your first post that catches my attention. The mentioning of that tank should not have rusted this quickly. Is the pond constructed of metal?

 

[GBBUDD]

it is the natural process of decaying matter . if you take a stick or your finger and it jumps away from your finger it is NATURAL oils from decay. if it sticks to your finger then it is a man made oil and it needs to be removed and the source needs to be found. the easiest way to remove it is with just a little bucket and just sink the edge of the bucket next to the film and skim the surface. if it runs away from your finger it wont' hurt your fish except there is an inballance somewhere and algae blooms could be next

 

[Tula]

it is the natural process of decaying matter . if you take a stick or your finger and it jumps away from your finger it is NATURAL oils from decay. if it sticks to your finger then it is a man made oil and it needs to be removed and the source needs to be found. the easiest way to remove it is with just a little bucket and just sink the edge of the bucket next to the film and skim the surface. if it runs away from your finger it wont' hurt your fish except there is an inballance somewhere and algae blooms could be next

Very interesting information about natural decaying matter being repelled from an object, I never knew that