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So I've noticed that my 72G cichlid tank very quickly after a water change starts to form a kind of 'oil slick' coating on the surface of the water.

It does not seem to affect the water chem, as all parameters seem ok. Nor does it seem to affect any of the fish, as they are thriving.

I do 30-40% WC's every 10-14 days - tank has been stable and healthy for just about a year straight.

What is this oil slick? Could it just be the remnants of the floating food pellets that dissolve? That's my first guess, but I wan't to make sure its not something more worrying.

Thanks.

72G Bowfront. 1 Sunshine Peacock, 2 Yellow Labs, 1 Ps. Elongatus, 1 Blue Ahli, 1 Red Kadanga, 1 Mel. Exasperatus, 1 metriaclima emmiltos, 1 Ancistrus.

14.5G 4 Neon Tetras.

It sounds like a biofilm. It is most likely proteins and bacteria, nothing harmful.

You can remove it by laying butchers paper (any unprinted paper really) over the surface of the water and then pulling it away. The film sticks to the paper.

Increasing surface agitation should also do the trick.

I'd suggest maybe feeding a bit sparingly directly after a water change, and until this problem clears up Have you changed foods recently? Are the filters not moving the water surface the same way? Anything different?

For animals, the entire universe has been neatly divided into things to (a) mate with, (b) eat, (c) run away from, and (d) rocks. - Terry Pratchett

I did start using a new spirulina pellet.

I feed only once a day, and its not a huge amount, just enough to keep the boys lean and mean. I get very little food debris left over (if any), and my pleco takes care of what does get missed.

There's been no change in the filter - although I did lower the spray bar to prevent some splash on the hood....I still get movement, but no real surface breaks in the water.

Hmmmmmm.....maybe I should raise the spray bar a bit, create some surface breaks again?

I'm having a eureka moment here!!!

Thanks Callatya!!!

72G Bowfront. 1 Sunshine Peacock, 2 Yellow Labs, 1 Ps. Elongatus, 1 Blue Ahli, 1 Red Kadanga, 1 Mel. Exasperatus, 1 metriaclima emmiltos, 1 Ancistrus.

14.5G 4 Neon Tetras.

Hi,
The "oil slick" is the result of the various types
of fish foods that you are using. Most contain protein,
and may contain fish oils. Additionally, any cooking
such as fried foods, smoke from the kitchen, cigarette
pipe or cigar smoking etc.
The result is the film that you see on the surface.

To rid the tank of it, you can turn off the circulation
and then lay paper towels on the surface of the water.
Just touch the towel to the calm surface and then remove
and discard the towel. Keep doing this till the surface
is clean and then restart the circulation.

Another way to rid the tank of the slick is to increase
the surface agitation with the spray bar as you mention,
and add to that with an air stone, etc. The slick will
combine with dust particles from the room the tank is in
and with the debris within the tank and settle to the
bottom where it will be vacuumed up during the regular
water changes.

To lessen, or eliminate it in the future, check the labels
on the fish foods and use those with smaller values of
fish oils. Feed less at a time, and clean the tank
regularly. And lastly, use a good fitting top on the
aquarium to keep the household causes out of the tank.

Frank

-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

Hey Frank - I've been debating adding an airstone for a while now...but wasn't sure if that would agitate the already tempermental cichlids?

I'll definitely consider adding one - I've always liked the effect it adds.

Btw...no smoking or fried foods, so I guess being health conscious not only benefits me but my fish as well!!!!

72G Bowfront. 1 Sunshine Peacock, 2 Yellow Labs, 1 Ps. Elongatus, 1 Blue Ahli, 1 Red Kadanga, 1 Mel. Exasperatus, 1 metriaclima emmiltos, 1 Ancistrus.

14.5G 4 Neon Tetras.

I have seen it in my 45lt Cardinal tank several times and usually goes within 24 hrs.

If it is always after a water change collect some water in a glass and check it to make sure it is not coming through your water supply.
If you use an air wand the bubbles will not be as strong and they will be spread over a larger area.

Have a look in [link=My Profile] http://www.fishprofiles.com/forums/member.aspx?id=1935[/link] for my tank info
Look here for my
Betta 11Gal Desktop & Placidity 5ft Community Tank Photos

Keith

Near enough is not good enough, therefore good enough is not near enough, and only your best will do.
I VOTE DO YOU if not WHY NOT?
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Hey all,

Oil slick has been resolved. Just raising the spray bar was enough. Now I get a smattering of air bubbles that break the surface.

Thanks all!

72G Bowfront. 1 Sunshine Peacock, 2 Yellow Labs, 1 Ps. Elongatus, 1 Blue Ahli, 1 Red Kadanga, 1 Mel. Exasperatus, 1 metriaclima emmiltos, 1 Ancistrus.

14.5G 4 Neon Tetras.