help with geothermal pond

[ryanw]

I purchased a house in MI. USA late fall and it has an open loop geothermal system which pumps water from a well through the heat exchanger in the furnace then dumps it to a decorative pond. It has an overflow drain in the pump chamber that feeds two larger holding ponds. the decorative pond has a nice design with two waterfalls, and I hope to add some fish this spring. I know there were some lily pads and tons of frogs, but I'm not sure what others plants were present. It was not protected from leaves last fall and is quite full of debris. It never developed ice over the surface due to the constant flow of water but it did develop quite a bit of algae.

I'm not new to water chemistry and have kept fish only and planted tanks for the last 20 years.

What steps should I take this spring to rehab the pond? It's a unique situation because when the furnace or air conditioner is on the water is flowing through the pond. Anything I add will simply be washed away, but yet there will periods of time from 1 day to maybe a month or more where no new water will be added.

My initial plan is to drain most of the water and shovel the debris out. I plan to add some biological type filtration but I doubt I need it with the two waterfalls. For livestock I will start with something inexpensive because I did notice a mink catching frogs over the winter.

Thanks for your help

 

[Meyer Jordan]

Since your source water is a well and this will be a flow-through system the majority of the time (I assume), it is recommended that a schedule of water tests (weekly, monthly, etc.) be set up to determine the water quality coming from the well. Unlike commercially sourced water, well water is subject to rapid changes.

How does this system affect the water temperature of the pond? Is the temperature raised during the operation of the heater/AC? If so, how much?

 

[ryanw]

The well water parameters are very consistent. It's fairly hard, but nothing remarkable. I've tested it a few times for another of my interests, brewing beer.

For temperature change I'm not sure on the AC since we haven't reached cooling season yet, but I believe it will be 7 degrees F warmer than the input temp which is right around 50F. The reverse is true for heating, the exit water is around 43F.

I'm not sure how we will use the system yet, but we may not use the furnace or AC for April/May then may intermittently use the AC for the rest of the summer. It's those intermittent periods that have me a bit worried.

 

[Meyer Jordan]

It's those intermittent periods that have me a bit worried.

This is why I asked about the water temperature of the output.
You may have a problem. Abrupt, sizable changes in water temperature are a major stressor for fish. The general consensus seems to be that sudden temperature changes should never exceed 5C (8F). Your's appears to be border-line.

 

[ryanw]

It's not important what the temperature of the incoming water is, it's the difference between the existing temp of the pond and the incoming water. If the temjp of the pond raises into the 70s in July then is hit by 57F water from the AC, that makes a big difference. If I wasn't clear before there is no water flowing to the pond unless the furnace or AC is running.

 

[Meyer Jordan]

It's not important what the temperature of the incoming water is, it's the difference between the existing temp of the pond and the incoming water. If the temjp of the pond raises into the 70s in July then is hit by 57F water from the AC, that makes a big difference. If I wasn't clear before there is no water flowing to the pond unless the furnace or AC is running.

I was thinking only of whenever the furnace/AC usage begins. This is when any major changes in pond temperature will take place. Close monitoring may be indicated. If it was me, I would disconnect the pond from the system.