Lakes and Ponds – Chapter 9 | Texas Aquatic Science

T1 - Investigations on photosynthesis and mineralization in experimental ponds

Lakes and ponds are inland bodies of standing or slowly moving water

Water quality is one of the most overlooked aspects of pond management - until it affects fish production. Clay turbidity in ponds is one of the most common quality issues we address (see by in Ag News and Views, May 2009). However, several other variables influence water quality for fish including water temperature, phytoplankton, photosynthesis and pH, carbon dioxide, alkalinity and hardness. Additionally, water quality can be affected through the interaction of these factors.

Plankton which account for most of the photosynthesis on Earth found in lakes, ponds and oceans

The Effect of Algae on the pH | Healthfully

If your GH is low this can be a problem (with a stable pH) during the hours of the day when photosynthesis is high, even with an adequate KH.
It is possible in a pond with heavy plant growth and/or high algae growth WITHOUT adequate water hardness (GH), for aquarium chemistry to become problematic due to increased photosynthesis. So either the reduction of algae and/or an increase in minerals to aid GH is important if GH, pH, or KH are problematic.

Products such as Wonder Shells can help with supplying essential mineral cations (as well as stress from transfer and poor osmoregulation)

For more about how this affects algae, please follow this article:

For more about Alkalinity and hardness in ponds, please read this outside resource:

I recommend reading these articles for more about the aspect of mineral ions, KH, GH, & pH:

Generally most Pond Fish such as Koi and Goldfish like a higher ph of about 7.8 (although a pH in the range of 6.8 to 8.0 is often acceptable). A well planted stable pond usually does not have problems with too high or too low a pH.

goldfish kept in ponds prefer a higher alkalinity and pH).
If your pH is too low/unstable, Sea Chem Buffer can improve the stability (I recommend the Marine version since the Koi and . For large volumes of water, aragonite may be more cost effective (Oyster shells are too slow to dissolve and do not work well from my experience).
However I do NOT recommend the use of Plaster of Paris or lime (CaO) as this is not balanced and not add the other necessary elements such as Magnesium, carbonates.
Further Reference:

For too high a pH (rare), these are cost effective ways in a pond:

Lakes and Ponds Lessons from Biologists: Pond Experts & Pond Habitat Biologists.

A pond’s oxygen levels can vary widely over the course of a day. This happens because during the day air from the surface and oxygen from plants is constantly replenishing the dissolved oxygen consumed by animals and by aerobic decomposition of detritus and other decaying matter. Plants stop producing oxygen at night because photosynthesis requires sunlight. During the night oxygen continues to be used by animals and aerobic decomposition. This results in many ponds having higher dissolved oxygen levels in the day than at night.

How to Show Oxygen Is a By Product of Photosynthesis

Aquatic and Wetland Plants in Florida – Plant …

In oceans, ponds, lakes, and other aquatic enviroments, photosynthetic organisms include (B) multicellular algae, such as kelp; (C) some unicellular protists, such as Euglena; (D) and the prokaryotes called cyanobacteria; and (E) other photosynthetic prokaryotes, such as these purple sulfur bacteria (C, D, E; LMs).

Pond Aeration Systems & Lake Fountains | Vertex Water Features

The result of any pH test is only an indication, as the pH can vary at different times of the day depending upon photosynthesis and the respiration of flora and fauna. To get an average reading, it is best to test the pH level early in the morning when it will be at its lowest and again at dusk when it will be at its highest. The majority of ponds tend to be on the acid side, but if your average readings suggest your pond is on the alkaline side, you can still use Aquaplancton, in these cases the pH tends to stay about the same and in any case will not increase beyond a maximum of 8.3 which is within the comfort scale for your fish. If the pH is less than 5.0 or higher than 11.0 it is unlikely that your fish will survive.