We recently dug a 1/4 acre pond on a remote island in the Bahamas, the pond water has a strong tea color to it and the sludge on the bottom of the pond gives it a very nasty deep brown color. We would like to try to clean the water/ pond and would appreciate any help that anyone might be able to offer.

The water itself is brackish and the pond has a very fine sandy bottom, the pond is around 5’ deep (approx. 500,000 gals) and there's a good layer of organic material that settled since we excavated back in November 2014. The sediment layer seems to be around 2' deep in places. The water temp is around 76-80 degs. year round and the pond/ lagoon is fed by a fresh-water lens along with any rainfall that we pick up (it is the dry season here at the moment).

I'm told the brown coloration is due to all the tannins from the organic material on the bottom, we would like to explore (non-chemical) solution to cleaning the water, but don't know where to start... aeration? filtration? sludge pumping?? Not sure.

I will upload a couple of photos and would really appreciate any feedback.

Thank you in advance!

NickD

Welcome to PB Nick.

It could be tannins. Is there anyplace to send a sample to have the water tested? If it is, any fish stocked will die.

Been there, done that.

Hi Dave - Thank you for the nice welcome and the prompt reply.

I thought about sending a sample back to the States to be analysed, but I read that you have to keep the sample cold for it to be effective so shipping from here would be problematic. Is there a self testing kit that I could buy online that you would recommend? From all I've read, I'm pretty sure that tannins is our problem, but a test would be useful.

Thanks again for the help.

I have not heard about keeping the H2O samples cold. I sent 3 samples from Hawaii to Texas A&M for testing. No problems.

There probably is a test kit but I don't know anything about those. I've just sent one to Texas A&M and having cold water in Texas is unusual.

You can do a small test by just buying a couple of minnows, putting them in a bucketful of the water, small aquarium, etc and see what happens.

Thanks roadwarriorsvt I may have got bad information about that then, I think I'll send a sample out for testing and see what we get back. I appreciate the advice.

Wow, Turks and Caicos. Been wanting to dive there for years.

Water definitely looks like tannins. Looks like the water in the Cenotes in Mexico. Tannins (tannnic acid) are acidic because if they are strong enough in the cenotes they will even etch the plating on the hose ends of a scuba diving regulator.

So it would seem that limestone to neutralize the acid would be helpful for the water, but that is just a guess on my part. Of course the tannic acid like you said is produced by the organic matter (leaves from trees in the cenotes) so removing that would also be helpful.

Maybe I need to come down and take a look. Any good reefs nearby?

Tannins tend to make the water acidic. In theory you could test the PH with a pool or hot tub strip to get an idea.

Calcium carbonate or crushed sea shells will absorb the tannins and neutralize them. Depending on the mesh size of the product added the faster the reaction will be in clearing up the water. Most likely this could be a maintenance thing if the tannins are leaching in from other sources.

Test in a bucket and take a look. A quick test if you do not have any PH paper is add house hold ammonia to a bucket of pond water. Just a tea spoon at a time. It should go murky then titrate like snow to the bottom of the bucket. This will give you an idea of the PH. If the PH is high the ammonia will have no effect on the water. If you put to much ammonia in to fast it will have little to no effect on the water. Slow and steady.

Cheers Don.

Say Hi to John Ramsey for me while you are there. He has a nice place on T&C, you will probably run into him there. I know he runs/owns a radio station or two, maybe a few other things. I haven't spoken with him in a while.

Welcome, Nick! When you said your pond is "brackish", that mean a high salt content, and it may be possible there is a high saline level considering your location. If Tannins are the culprit for the brown staining, about all you can do is identify, remove and replace the offending plant life that is causing the staining. You could filter the water, but that would be a pretty pricey endeavor. I am guessing the "sludge" you have on the bottom is from the very steep sides sloughing off. I would bet you soil is mostly sand and decayed leaf litter with all that lush vegetation in the pictures.

The tannins themselves are not harmful, but the acidic environment that usually leaches the tannins out of plant life is often very hard on fish. Do a pH test first, or get your water sampled as mentioned earlier. If you can get Ag Lime or bags of pelleted lime, that would be probably be a huge benefit. Clearing some of the trees from the edges and replacing with a grass fliter will help a lot also!

Just how salty is it, too salty for freshwater fish?

If so, a large number of saltwater fish will do fine in low salinity once you get your tannins figured out.

Do you have a way to suck out the bottom or dig it out more.

Do you actually see leaves etc on the bottom or just silt?

Mine was caused by putting a bunch of cleared oaks in the bottom for cover. The water turned lethal. I pumped it dry and let the Texas summer clear up everything. It might not dry out in the Bahamas.