School Ponds Need Help, Please

[HoyasNCrypts]

I humbly request any suggestions that may aid in our current struggle:

I work at a school in Northeastern Florida, and I inherited the care of 2 small ponds, located at the entrance to one of our buildings. The ponds are about 6.5-7 feet around, and about 2.5-3 feet deep when full.  The only permanent residents are goldfish, which we've kept (relatively) successfully for a couple years. 

For some reason, these ponds were built without filters- only water pumps. The pumps just power the waterfalls. 

We've slowly grown more and more dark, black algae, which is beginning to take over, and looks pretty unsightly. That algae, I assume, is aiding in filtration in a major way, because... as mentioned, the ponds were made without filters. 

In an effort to provide some sort of functional mechanical/biological filtration, I put together a crude system which somewhat works, a little, and is better than nothing: I ordered 200 plastic pot scrubbers off Amazon, along with mesh bags.  I filled the mesh bags with the pot scrubbers. I cut the bottom off a large plastic crate, filled the crate with the bagged pot scrubbers, and placed the whole thing over the pump. I then put rocks on top of the sponge-filled crate to hold everything down (these components, along with the ponds themselves, are pictured below). 

I hoped these "filters" would work, sucking the water through the bags of sponges on it's way in, and coming out and over the waterfall "clean".

And I think they are working, to an extent. Any time I go in to gently clean them, they're covered in the delightful brown sludge- seemingly housing a thriving colony of beneficial bacteria. 

But I just don't think it's enough. 

The ponds have tons of algae. And I know- goldfish produce a lot of dirty waste. The ponds are both covered by a roof, meaning- because of the shape of their build and their location- even in the peak of summer, they only receive a few hours of indirect sunlight per day. This has made growing plants challenging (I also just may not be great at growing plants in a pond). I did manage to add some Canna Lilies, a Peace Lily, and a few epiphytes, which do what they can to help.

As you can see from the picture, the pH is testing at LEAST at an 8.8. An ammonia test, however, revealed very little ammonia (assuming I performed the test accurately- dip the strip completely in and out of the water for 30 seconds, check reading). 

I've tried hooking up a canister filter, but the fact that the ponds are (slightly) lower than ground level, made it very difficult, almost impossible, to get it to run properly.

I own 1 aquarium that's run fairly successfully for a few years now, but don't have any experience with ponds, other than what I've learned trying to help out with these 2. 

I appreciate everyone's time, and will gratefully accept and try any potential solutions. 

[Guppysnail]

I’m not a pond person so do not have direct advice.

Our club formed a partnership with a local school. One of the offered extracurricular clubs is now a freshwater fish club members oversee.  The club uses that school pond to help educate young folks and the school gets the pond well maintained.  The club also offers scholarship grant money to students for college. 
Though you may not be able to form this type of program you may want to reach out to local clubs.  Fish enthusiasts are always willing to help and they may even do a club event to come help set up something better for you. 
 

Club locator on ACO store home page at the bottom. 

[Creedmoor Aquatics]

I'd start by saying if the fish are healthy, that's great! You can take your time and make gradual improvements for the benefit of the pond and the students. 

The next thing I'll say is if your goal is ultimately reducing the amount of algae in the pond then you need to be thinking in terms of nutrient export. Right now there is a lot of nutrient in the pond that has been bound up in the algae. If you introduce something that will kill the algae, you'll be releasing all of that nutrient into the water where it may be harmful to the fish, and if not removed will ultimately just become food for more algae. 

This is also not a problem that developed overnight, so your solution does not have to take effect overnight either. If you can continually 'starve' the algae of nutrients it will slowly recede. 

One straightforward method of accomplishing the nutrient export is to simply change water. Either by regularly performing water changes, or implementing a continuous water change system where water is continuously added to the pond, and above a certain level, continuously drains out. This isn't necessarily the 'easy' option, but it doesn't require any overt changes to the pond. 

You would ideally fast growing floating plants to draw nutrients out of the water, and then remove and dispose of a portion of the plants. Depending on how often you are able to access the site this is in some ways easier than performing water changes, and in the long-term can prove more stable and effective. Water hyacinth is still banned in Florida and you won't be able to get a permit for water lettuce either. Duckweed would work well, though goldfish often love eating it so you may struggle to keep it in the pond. This is one where I'd check with locals to see what floating plants they often keep.

Water lilies might not grow particularly fast, but they will help shade the pond which will also help control algae.

Two (non-floating) plants I *would* recommend would be pickerelweed (Pontederia cordata) and duck potato (Sagittaria lancifolia), both native species that are both fast growing and excellent for absorbing nutrients. 

The *fast* way, if the algae has really become an eyesore and needs to be fixed sooner rather than later would be to remove the goldfish, drain the pond, and then spray the algae down with hydrogen peroxide. Leave for fifteen minutes then wash everything in the pond down and do several large water changes before re-filling the pond and adding the goldfish back in. Try and really stir up the muck in the gravel as you're doing the water changes to clean it as much as possible. Then be on standby to do more water changes in the next days and weeks as the algae all dies and releases its nutrient into the water. 

[DallasCowboys16]

On 1/22/2024 at 7:27 PM, Creedmoor Aquatics said:

I'd start by saying if the fish are healthy, that's great! You can take your time and make gradual improvements for the benefit of the pond and the students. 

The next thing I'll say is if your goal is ultimately reducing the amount of algae in the pond then you need to be thinking in terms of nutrient export. Right now there is a lot of nutrient in the pond that has been bound up in the algae. If you introduce something that will kill the algae, you'll be releasing all of that nutrient into the water where it may be harmful to the fish, and if not removed will ultimately just become food for more algae. 

This is also not a problem that developed overnight, so your solution does not have to take effect overnight either. If you can continually 'starve' the algae of nutrients it will slowly recede. 

One straightforward method of accomplishing the nutrient export is to simply change water. Either by regularly performing water changes, or implementing a continuous water change system where water is continuously added to the pond, and above a certain level, continuously drains out. This isn't necessarily the 'easy' option, but it doesn't require any overt changes to the pond. 

You would ideally fast growing floating plants to draw nutrients out of the water, and then remove and dispose of a portion of the plants. Depending on how often you are able to access the site this is in some ways easier than performing water changes, and in the long-term can prove more stable and effective. Water hyacinth is still banned in Florida and you won't be able to get a permit for water lettuce either. Duckweed would work well, though goldfish often love eating it so you may struggle to keep it in the pond. This is one where I'd check with locals to see what floating plants they often keep.

Water lilies might not grow particularly fast, but they will help shade the pond which will also help control algae.

Two (non-floating) plants I *would* recommend would be pickerelweed (Pontederia cordata) and duck potato (Sagittaria lancifolia), both native species that are both fast growing and excellent for absorbing nutrients. 

The *fast* way, if the algae has really become an eyesore and needs to be fixed sooner rather than later would be to remove the goldfish, drain the pond, and then spray the algae down with hydrogen peroxide. Leave for fifteen minutes then wash everything in the pond down and do several large water changes before re-filling the pond and adding the goldfish back in. Try and really stir up the muck in the gravel as you're doing the water changes to clean it as much as possible. Then be on standby to do more water changes in the next days and weeks as the algae all dies and releases its nutrient into the water. 

I would agree here. A good drain and scrub would help to "reset" the ponds which seem to be pretty chock full of detritus at this point. Battling algae in the current situation will likely be a losing battle.

An aggressive scrub and large water change a few weeks in a row would likely help tremendously.

From there I would agree that introducing some fast growing nitrate absorbing plants would help to create a healthier situation long term.

Edited January 23 by DallasCowboys16