Soil substrate pond

[cas]

I love the information in this thread. I had to go back and reread it from the beginning.

 

[MitchM]

We're now at the 10 month mark for the greenhouse "ponds".

I have done very little other than top off water, feed the fish and some plant pruning.
I have never cleaned the glass.
I added 2 6" koi about 1 month ago and they're doing fine with pretty much no impact on the plants and substrate so far.
In the garden soil substrate you can see lots of yellow and green, signs of fungi and cyanobacteria, important components of a healthy substrate that breaks down organic components into chemical forms that are available for the plant roots and maintain an overall healthy chemical balance.

In the upper pond, there has been no sign of string algae. I think the presence of the constructed wetland filter, with a substrate of gravel and clay is the main reason. The goldfish are also constantly eating any algae that appears. Clay is a known adsorber of phosphorous, a contributor to string algae growth. That is an indication that adding clay to an existing system is worthwhile.
In the lower tank, string algae is the prevalent plant. There is no constructed wetland filter hooked up to that system. Harvesting it is simple and exports excess nutrients.
I still remain impressed on how maintenance free both systems are.

There are 2 shubunkins and 2 koi in the upper tank and 3 rosy red minnows in the lower tank. The rosy red minnows are getting to be the size of small goldfish.

Questions, criticisms, requests for further clarifications are welcome.

 

[MitchM]

One thing that stands out for me is that there is very little, if any, periphyton.

 

[Meyer Jordan]

One thing that stands out for me is that there is very little, if any, periphyton.

Which indicates that the systems are oligotrophic (low nutrient).

 

[MitchM]

That's what I thought.
So I've started daily feeding with flake food to see what happens.
The fish seem well nourished at this point.

 

[MitchM]

Which indicates that the systems are oligotrophic (low nutrient).

Could a healthy submerged plant population not simply replace the presence of periphyton?

 

[Meyer Jordan]

Could a healthy submerged plant population not simply replace the presence of periphyton?

Possibly, but not likely. In fact, periphyton is present on many oligotrophic systems. Is there epiphytic growth on the plant foliage?

 

[MitchM]

Yes. The goldfish and koi constantly graze on it.
The minnows do not.

 

[Meyer Jordan]

Yes. The goldfish and koi constantly graze on it.
The minnows do not.

That is one form of periphyton. What is the percentage of sand in your sub-strates? Biofilm on sand is of a completely different composition than that any other sub-strate and usually the weakest as to nutrient adsoprtion. It will not usually support any algal growth.

 

[MitchM]

No sand that I'm aware of.
There is a 1 inch cap of 7mm gravel on top of the soil.

 

[MitchM]

Here is a picture of the tropical tank with a healthy growth of periphyton on the substrate, I have only cleaned the glass twice in the last 6 months.
Same substrate, same gravel cap, warmer temperatures, heavier feeding regime.
The temperature in the tropical tank is a steady 27C, while the greenhouse tanks vary between 11C and 17C.
There is no clay wetlands filter in this setup.

 

[Meyer Jordan]

Temperature is obviously playing a large role here.
"Response of periphytic algae was measured as changes in biomass, diversity, biovolume, and growth rate during a seven-day colonization period. Maximum biomass developed at 27 °C during early stages of colonization and optimum temperature associated with maximum biomass shifted later to 33 °C."
TEMPERATURE ELEVATION DRIVES BIOMASS AND COMMUNITY SHIFTS IN PERIPHYTON
Nana He

 

[MitchM]

Thanks for that reference.
I've found Nana He's thesis online and am reading through it.

 

[MitchM]

Based on a discussion in the water changes thread, I tested my GH, KH, PH and salinity in both the source tap water and the substrate pond with a wetlands filter. Measurements taken at 2PM, full sun. I'll test PH again early tomorrow morning.
I'm concerned that the low KH reading may allow for an unhealthy change in PH value.

Substrate pond Tap water

PH 8.3 7.6
KH 17.9 ppm 17.9 ppm (both very low)
GH 350 ppm 400 ppm
Salinity 0 % 0 %

I attribute the low KH and the higher PH in the pond vs the source water from the fact that I have not shock chlorinated my well for a few years which has allowed for the buildup of iron bacteria and CO2, which gets off gassed once in the circulating pond system. Off gassing CO2 will raise the PH.

I have noticed no buildup of minerals in the no-water change substrate pond.

.

 

[MitchM]

Ph reading this morning at 6:30AM is 8.2, so no large PH swing.
The low KH is an accident waiting to happen though, so I'm going to add enough baking soda over the next few days to bring the kH up to 150 - 200 ppm.