Water Quality and Nitrogen Cycle

By now, you and your students have run tens of water quality tests. Let’s take a moment to slow down and look at what’s going on and why.

Nitrogen Cycle

Your aquarium is producing “waste”, including fish poop, uneaten food, and dead fish. The Nitrogen Cycle is the biological process that converts toxic compounds into beneficial bacteria colonies:

Waste → Ammonia (toxic) → Nitrite (toxic) → Nitrate (okay)

In the beginning, we added a weekly dose of biological enhancer (MicrobeLift Special Blend) to help these beneficial bacteria colonies form in our coldwater ecosystem.

(If we had plants in the aquarium, they would absorb these nitrates and use them as nutrients, completing the cycle. Since we don't, we can do partial water changes regularly.)

The video here might be familiar to some of you. This example by Aquarium Co-op explains the Nitrogen cycle using m&m’s. You can use this video with your students, or another one that you may prefer more. 

How To Run A Full Water Quality Test

This video features our very own Phil Koon, showing the entire process of running a full water quality test. Ideally, we’re doing this every other day to have an accurate reading of our water trends.

Recording Water Quality Data

Not only do we want to be testing our data, but we want to be recording it as well. This helps us keep an accurate record, and can show the students these biological processes in real time. You can print out and keep this Trout Care Daily/Weekly Checklist nearby your aquarium for the students to help fill out. As the teacher, you will also be uploading this information into the 2025-26 Aquarium Monitoring Data Sheet, so the DCL team has access to this information and can help you troubleshoot any issues that may occur.

Recommended Water Testing Levels:

• Ammonia- Less than 1 mg/l (ppm).

• Nitrite- Near zero (ppm), once bacteria are established in the filter system

• Nitrate- Below 40 ppm (mg/l)

• pH- The pH scale runs from 1 (acid) to 14 (basic).  7 is “neutral”.  A pH of 7.4 – 8.4 is fine for our trout

Ammonia and Nitrite at high levels are toxic to your fish. Nitrate is not, it would take up to 200 ppm for nitrate to be toxic.

What To Do if Levels are Consistently High (Over Extended Testing):

• If ammonia or nitrite levels rise above 1 ppm for an extended period, contact us.  Reducing or temporarily pausing your feeding schedule is a good first step that you can take right away.  Depending on the conditions in your aquarium, additional filter media or aquarium cleaning/gravel vacuuming can also quickly reduce these waste products.

• Nitrate levels will steadily rise during the year.  Without the presence of plants in our aquarium, the nitrogen cycle is incomplete, and there is no place for nitrate to go.  This is not a threat to your trout, but high levels will encourage algae growth, odor, etc. The only way to reduce nitrate is with partial water changes.

More Troubleshooting:

Depending on where you are consistently seeing concerningly high levels in your aquarium, you may need to troubleshoot further as to what could be the cause. A really great resource for troubleshooting is this Pennsylvania Trout in the Classroom document. It provides a great overview of the Nitrogen Cycle, and if you skip over to pages 56-58, you can find causes and remedies for high Ammonia and Nitrite levels that may help target and fix your exact issue!

Cannibalism

Check out this photo from Elizabeth Ann Clune Montessori School, where you can see a tail fin sticking out of a trout's mouth!

You and your students know that the trout are carnivores, and this means they’ll even eat members of their own species. It will take them a while to fully eat what’s in their mouth, so you might see that fin throughout the rest of the school day. If you see something similar at your school, take a picture and send it in!

This is the circle of life, so even if it seems sad, it’s an opportunity to learn about our finned friends. The ones that want to move on from fish food to live food indicate their ability to survive in the wild. Keep an eye on the ones that grow bigger than the rest if you want to see it in action.

 What Else Do Trout Eat?

We’re wrapping up the Live Food Experiment this week, so let’s recap all the fun things we learned and how the experiments went for each school!

Our Data

Here are some observations the students made while running the experiment:

1. Did our teacher feed the fish already today?

2. Does the behavior of our trout seem calm or stressed?

3. What if we added an underwater camera to observe the fish, to reduce the anxiety of being watched?

4. Did it just spit up a daphnia?

5. Did it actually eat 45 daphnia, or has it been breathing?

6. It ate 0 daphnia today, does this mean it will never eat live food?

7. Why is the experiment exactly 6 minutes long?

Look at all this critical thinking! Your students were able to recognize different variables that could impact their experiment.

What Do Trout Eat?

The trout we raise are strictly carnivores, and are opportunistic feeders. This means, they’re able to adapt to eat available food. Here’s a list of food your trout might eat in nature:

• Macroinvertebrates 

• Dragonflies, stoneflies, caddisflies, mayflies, snails, worms, and more

• Other (smaller) fish and eggs

• This is why you might see cannibalism in the aquarium!

• Crustaceans

• Crayfish and scuds

• Amphibians

• Frogs and salamanders

• Mammals

• Mice and young mink

• Remember…our trout are opportunistic!

Common (incorrect) answers:

Krill

Krill was a common thought among students this year! Although they live in the ocean and, therefore, can’t be trout food, it’s not a bad guess. Krill are also zooplankton and crustaceans. This shows us that the students were able to recognize what kind of food trout might be attracted to.

Krill vs Daphnia

Algae

This answer tells us that students know trout search for something plentiful and smaller than themselves. This month, they learned that trout are carnivores, and don’t purposefully eat algae.

Rocks

Our trout don’t want to eat something that’s not nutritious!

Use the sheet below to play a game with your students! Would My Trout Eat This?

Daphnia!

Now that we have officially started our LIVE FOOD EXPERIMENTS, let’s take a closer look into the animal that makes it possible.

Daphnia are a small animal known as zooplankton. Their tiny size makes them a great snack for out trout, but also other creatures like macroinvertebrate larva. There are over 100 known species of daphnia! Trout in the classroom has used a few different kinds for our experiments over the years. These colonies can produce both sexually and asexually! Female daphnia can also release their eggs into the sediment where they sit dormant for upwards of 80 years before the right conditions allow them to hatch.

If your school hasn’t run the experiment yet, check out this video of the way they “jump” through the water!

So, what do Daphnia eat? Well, they’re herbivores! They eat phytoplankton, or “algae” that use the sun’s energy for photosynthesis. Phytoplankton come in all different shapes and colors, but they’re often GREEN.

Here is a picture of what I feed our colonies during the month! With a microscope, you can actually see their gut, which is clear, full of food. Daphnia are critical for controlling algal populations.

Phytoplankton can grow so intensely, they become known as an algal bloom. Check out these pictures in Owasko Lake (left) and Fall Creek (right). This can be exacerbated by human impact. Adding excess nutrients, such as fertilizer runoff or sewage/animal poop, have caused these blooms to worsen. Why is this bad?

• Harmful to human health

• Harmful to pet (including dog) health

• Depletes oxygen and kills fish and other organisms

• Blocks sun from reaching organisms deeper in the water

Daphnia are an amazing species. They are sensitive to pollution and, therefore, incredibly helpful in determining the health of a body of water.

Dapnia present? Healthy water! Daphnia are absent? Check out the water more.

This is known as an indicator species!

We might not spend the year studying daphnia, but they're helpful to learn about when considering the ecosystem for our trout. All of these factors come together to create a healthy habitat for us and the animals we live by.

What's In My Aquarium?

Now is a great time to refamiliarize ourselves with what’s in our aquarium, how they support our trout, and solutions to common problems. All of your fish have survived the break, so here’s one more refresher for the new year!

Water Quality Levels

You all should be familiar with typical chem test levels, but here’s a reminder for the start of the year:

• Ammonia- Less than 1 mg/l (ppm).

• Nitrite- Near zero (ppm), once bacteria are established in the filter system

• Nitrate- Below 40 ppm (mg/l)

• pH- the pH scale runs from 1 (acid) to 14 (basic). 7 is "neutral".  A pH of 7.4 – 8.4 is fine for our trout

Keeping a record of your chem test levels is important! This way, you can see if something isn’t resolving.

Common Equipment Problems→ Solutions

FILTER

QUESTION: What do I do if the filter canister is making a loud/rattling noise or is hot to the touch?

This is an indication that water is not moving through the filter pump properly.

1. Locate the filter outflow nozzle just beneath the surface of the water in your tank. Check to see if water is flowing out by putting your finger in front of it.

If water is NOT flowing:    

1. Unplug your filter and let it cool down for 15 minutes.

2. Check to make sure that any screening over your outflow nozzle is clear of debris. Remove it and rinse off as needed. Check the water intake for the filter (at the end of the long plastic tube going to the bottom of your tank). If there is screening around the intake, make sure it is free of debris. Remove it, rinse off and replace. (All parts of the intake cage can be removed and replaced by hand. You won't break it!)

1. You can have students help with this! It’s good to have an extra set of hands holding the tube near the surface of the water, and swatting away fish that may get sucked in. 

3. After 15 minutes, restart your filter. First, locate the gray/red gently manual pump handle on the top of the filter canister. Pump it up and down several times. Water should flow out of the outflow nozzle when you pump. Plug in the filter, and evaluate. A few extra manual pump strokes may be necessary.

5. If the filter is still rattling, or not pumping water, you have a broken impeller or impeller shaft. Leave the filter unplugged. Call DCL, and we will come out to replace the piece.

CHILLER

QUESTION: My chiller isn’t functioning properly, what could be wrong?

For a variety of potential malfunctions, the first thing to do is to power down the unit (unplug or switch off) and wait 10 seconds before restarting.  This reset may do the trick; if not, call us.

QUESTION: My chiller is on, but water in the tank is not getting cold enough, what could be happening?

The chiller's "Pre-filter" may be clogged. This is a black foam cylinder attached to the submersible pump in your aquarium. If it has a lot of debris stuck to it, or appears to be squeezed together, it needs cleaning.

1. Follow the black cord from the submersible pump to the power supply and unplug it OR keep it running and have someone hold it near the surface to swat away fish while you continue with the following steps.

2. Pull the whole unit toward the surface, slide the foam filter cylinder off its frame and rinse it out.  

3. Replace the clean foam filter, PLUG THE PUMP IN IF YOU TURNED IT OFF.

4. You should notice an immediate increase in water flow through the chiller system. Your aquarium should begin to cool over the next 15-20 minutes

If these solutions don’t fix your chiller problem, call DCL and we’ll come out to help find a solution.

AIR PUMP

QUESTION: How come my blue air pump is buzzing but there are no bubbles coming from the airstone at the bottom of the aquarium?

1. To address noise, shift the pump away from any other surfaces.  Also make sure that the rubber feet on the bottom of the pump are in place.  

2. If no bubbles are rising from the airstone, follow the clear airline from the airstone to the blue air pump.  Make sure all connections are in place. Occasionally, they can be pulled apart, and can be easily reconnected by hand.

3. If neither of these options helps, unplug the airpump and call DCL. Your fish will be fine for several days.

Other Common Issues

1. If your intake/outflow cages don’t have netting on them, fish can get sucked in! While your trout are still small, make sure there is some type of filter preventing this

2. Ensure all intake and outflow tubes are secured! Sometimes, these can be bumped out of place and cause a leak.

3. If your fish are in a warm tank or being removed to fix a problem, you can tape/add a bag of ice to their temporary location to keep the temperature low!

Main Takeaways

1. If your filter is ratting and you can’t find a solution, unplug it

2. If your chiller isn’t cooling properly and cleaning/resetting it doesn’t work, call DCL

3. If your bubbler isn’t producing bubbles, check all connections are in place

A longer version of this review is in our Tech Support Tab in this blog post. It’s great to be able to troubleshoot, but if you’re worried about the health of your tank send an email to education@discovercayugalake.org AND bill@discovercayugalake.org