How do you tell about "doc"

[botiaboy]

I have a cycled 55 gallo tank which I am planing on having a few clown loaches in,and I'm saving for a bigger one.I read that clowns are sensitive to dissolved organic compounds,and I wanted to know how you test for those.

[Mark in Vancouver]

If there's a simple test for DOCs, I don't know about it. I think the issue is not so much the compounds that are actually dissolved in the water, but the buildup of mulm and waste matter in the substrate. Vacuum your substrate once a week and it won't be an issue.

Clown loaches are found in densely muddy waterways, in jungles, where the amount of organic matter floating free in the water would be intense. Because your tank system is closed, you just need to clean it out to prevent the buildup of ammonia and so on, which loaches are certainly sensitive to. That's an issue of removing fish and plant waste, though.

[Gary Herring]

Botiaboy,

As Mark said, DOC's are nowhere near as much to worry about as pollutants such as ammonia, nitrIte or even nitrAte. Having said that, if you have a really high level of them you are more liable to have problems with algae (the dreaded blue-green in particular) and reduced oxygen levels, as well as stress to the fish.
If you really are worried about dissolved organic's, there is a test you can perform to determin if the levels are to high - a 'biological oxygen demand' test. For this you will need a 'dissolved oxygen' test kit:

Take a sample of your water, and test it for dissolved oxygen as per the instructions on the test kit. Record the result.

Then take a second sample, making sure that there is no air in the test tube. This is essential for the accuracy of the test, and you can ensure this by filling the tube and sealing the cap under the water.

Store this second sample in a cool, dark place for 48 hours.

Then, after 48 hours, test the second sample for dissolved oxygen as you did the first.

Compare the results - if there is very little or no decrease, then your DOC level is probably OK. If there is a decrease in oxygen of more than 1mg/l, then your organic load is high and you should try to reduce it. You can do this by water changes and gravel vacuuming, etc, and basic good husbandry. Also, there are plenty of products availible to reduce and filter out DOC's. API's 'Bio-chem zorb' is one, or polyfilter. Probably just as good though,(and cheaper!) is plain 'ol activated carbon.

Hope this helps,

Gary