Pond chemistry - nitrite and phosphate spike, new to ponds but not aquatics - talk chemistry to me!


Joined
Jun 13, 2022
Messages
3
Reaction score
2
Country
United States
Hi there!

This is my first time posting on this forum, so please tell me if I'm in the wrong place. This is also a long post - bear with me! I want to really understand what's going on here, so please comment on and critique my thought processes and assumptions.

I work at a hobby farm doing animal care, and they recently started up a koi pond. I've worked professionally with aquatic systems before but only in tanks (saltwater and freshwater, laboratory research and educational displays - up to 2k gallons), so I'm adjusting to the less controlled settings of a pond! I'd really appreciate feedback on my thought process and what is going on here, as well as any advice/suggestions. In places where I'm estimating, it's because I'm not the owner, so I don't always know *exactly* when something was purchased or what it was. I only started helping in pond care recently because more attention has been focused on turning this into a koi pond.

Pond specs:
-Estimating 2.5k gallons
-Pump circulates through to a waterfall
-Filtration = skimmer basket and a filter pad below that/right above the pump. I've been rinsing them weekly, decent amount of muck in the filter pad but not really more than I'd expect. No other filtration, and the line from the pump to the waterfall is buried with no access points that I'm aware of, so I think it'd be hard to add something in-line like a UV filter :/
-Pond is in full sun and we are in Colorado (front range) so it's FULL sun, we have very few cloudy days
-Pond has been running for about a year
-6-8 small koi and goldfish (3-4 inches), 1 6in koi, 1 12in koi. 6 of the small fish were added several months ago, the 6in koi and a few more small fish were added maybe 3 or 4 weeks ago, and the 12in koi was added about a week ago. A few of the small fish have been found dead in the skimmer basket over the past few weeks. Maybe 2 or 3 total.
-We've added some pond plants, all have been in for at least a couple weeks now. 7 1-gallon pots (water lilies, some generic reeds, iris) and 2 1/2-gallon pots (horsetails)

All chemistry is from API kits (the liquid indicators, *not* the strips)

Chemistry from a week ago (tested the same 2 weeks ago too)
Ammonia: 0
Nitrite: 0
Nitrate: 0
Phospates: 0.25
pH: 7 in morning, maxing out (wide-range pH reads up to 9) in afternoon)
KH: 60ppm
Some foam around skimmer and in the basket

Interpretation: I feel like I *always* see at least some nitrates in tank systems, but the lack of nitrates here didn't really worry me, the pond has been going long enough and had fish in it long enough that I'm pretty confident it's cycled (plus no ammonia reading). There was a decent bit of algae growth (probably where the nitrates are going) which made sense with the phosphate reading plus the warming season and sunny weather. The wild pH swing was very concerning - assuming that is due to high algae load and lots of photosynthesis pulling out lots of CO2 during the day plus the really low KH not being able to buffer the pH.

Actions: made sure feeding was kept minimal. My employer bought a pH stabilizer from the local koi store (this product) and we dosed according to instructions. Also treated with a pond clarifier - I can't remember the specific product, it was one they already had so I figured I would use it up first. Generic "beneficial bacteria to help clear up pond scum" type thing. Tested the KH a few days later and it had gone up to 100ppm.

Chemistry from yesterday:
Ammonia: 0.25ppm
Nitrite: 0.25ppm
Nitrate: 20ppm
Phosphates: maxing out the test IMMEDIATELY (test reads to 10ppm), not needing any time to develop. So somewhere well above 10
pH: 7.5 in morning, 8.5 in afternoon
KH: didn't have opportunity to test
Foam mostly gone, really only inside the skimmer basket

Other factors - it's been really hot here lately, we're hitting 95-100 degrees most days. Sun beating down. There's also a tree nearby that flowered and has been dropping it's little flowers like crazy the last couple days (pretty sure it's a honey locust - small green flowers) I scooped a ton out of the skimmer box.

Interpretation: This has me a little freaked out. I'm used to treating nitrites as a HUGE red flag, immediate large water changes, etc. but I feel like I'm reading conflicting info about nitrites from resources about ponds - some people seem to have that "yikes" reaction and others seem like "meh, as long as they're below 0.5". All the nitrogen products seems to indicate a big addition of organic matter and/or fewer nitrogen products are being consumed. Nitrogen cycle is clealry still functioning so thank god for that. The nitrates are a comfy level, I'd prefer the ammonia to be 0 but 0.25 isn't panicking me, but the nitrites worry me.
And holy phosphates. I tested the hose water right away, it's reading at 0. Asked the owner about fertilizer applications in the area (there's some planted flowers around the pond) and he said there hasn't been any. So - presumably being produced internally. Similar to nitrates, either a lot more organic matter breaking down, and/or less is being consumed.
At least the pH is starting to stablize... but still not where we want to be.
Fish all still active, the big one likes to hang out in the deepest part near the bottom - not sure how normal that is. No one gasping or surface breathing.

Here's my hypotheses:
1. A lot of the algae has started dying off and decomposing. I feel like the algae has changed and looks more scummy than before, but I'm not used to looking at pond algae (sounds dumb to say that but please don't judge lol). Less consumption of nitrates + phosphates, and more production of nitrogen products and phosphates as it breaks down
2. All those itty bitty flowers falling in the water starting to breakdown - adding nitrogen products and phosphates
3. The heat is speeding up decompisition things are breaking down faster than they can be consumed.
4. All of the above?

Actions:
They don't own a pond vacuum. I did what water change I could, conscripting an industrial vacuum/mopper they have (it's a Waxie Versa, felt sort of ridiculous lol but it works. No chemicals on it, don't worry) which wasn't ideal but it allowed me to change probably a few hundred gallons. Sucked up algae and debris where I could but there's lots more left. That was all I had time for.

Feedback I'm hoping for:
-Are my thoughts and assumptions on the right track? Are there places where I could improve or correct my understanding?
-How worried should I be about the nitrite and phosphate spikes?
-What's the best path forward for bringing the nitrite and phosphate down?
-Anything else I should be doing to stabilize pH?
-Any other general advice on this setup?

I've attached several photos. I'm not sure if you can see the file names which have the dates in them... General pond photos from about a month ago, the pond from a week ago when the newest fish (the 12in koi) was added and where it's got some foam, and the scum/algae from yesterday as well as those little flowers that fell everywhere.

Thank you so much for taking the time to read and respond!

5-16 pond from end.jpeg
5-16 pond from side.jpeg
5-16 pond from waterfall.jpeg
6-7 large koi.jpeg
6-12 fallen flowers.jpeg
6-12 pond algae 2.jpeg
6-12 pond algae 3.jpeg
 
Ad

Advertisements

Joined
Oct 28, 2013
Messages
12,139
Reaction score
12,351
Location
Northern IL
Showcase(s):
1
OK - not a pond chemistry expert here, but a few observations:

From the photos, this looks smaller than a 2500 gal pond. I only mention that because it is important to know for purposes of bio load. The koi are small now, but they won't stay that way.

It appears you have DOC (the small amount of foaming). Perfectly normal if you do have organic material decaying in the pond but just something to watch.

You mentioned pond plants - I don't see any. Plants complete the pond trifecta - water, fish, plants - and your ecosystem won't be complete without them.

The amount of algae that you're seeing would not be a concern to me at all. Not pretty, but it's serving a purpose. With a brand new pond, patience is the best tool you can utilize. It can get ugly before it gets pretty!

Water changes are not really recommended in a pond. Mature water is your goal. Every time you remove mature water and replace with new, you change the balance again.

Again - there are others here who are better with the chemistry, so I won't even get involved in that. But kudos to you for recognizing that a pond is a whole different animal than an aquarium. They have water and fish in common, but that's about it!

Good luck to you and welcome to the GPF!
 
Joined
Jun 13, 2022
Messages
3
Reaction score
2
Country
United States
OK - not a pond chemistry expert here, but a few observations:

From the photos, this looks smaller than a 2500 gal pond. I only mention that because it is important to know for purposes of bio load. The koi are small now, but they won't stay that way.

It appears you have DOC (the small amount of foaming). Perfectly normal if you do have organic material decaying in the pond but just something to watch.

You mentioned pond plants - I don't see any. Plants complete the pond trifecta - water, fish, plants - and your ecosystem won't be complete without them.

The amount of algae that you're seeing would not be a concern to me at all. Not pretty, but it's serving a purpose. With a brand new pond, patience is the best tool you can utilize. It can get ugly before it gets pretty!

Water changes are not really recommended in a pond. Mature water is your goal. Every time you remove mature water and replace with new, you change the balance again.

Again - there are others here who are better with the chemistry, so I won't even get involved in that. But kudos to you for recognizing that a pond is a whole different animal than an aquarium. They have water and fish in common, but that's about it!

Good luck to you and welcome to the GPF!
Thank you for this! The pond is 20 feet long and 10 feet wide, and about 3 feet deep at the deepest point - but there's so many different pond calculators and I don't really know which are best so I definitely could be off.

Ha, I totally didn't realize that the photos of the whole pond are from before the plants were added, good catch. Ultimately, it's still not a lot of plants and it's pretty sparse.

That's a relief to hear about water changes and that makes sense. I've been trying to encourage the owners to see it as an ecosystem, so the patience concept really resonates with me. I keep worrying though that I'll miss something or not manage something right, and then the fish will die and I'll feel responsible :(
 
Joined
Oct 28, 2013
Messages
12,139
Reaction score
12,351
Location
Northern IL
Showcase(s):
1
We all share that worry - perfectly normal! Minimal intervention is the best approach. Keep the bio load low, avoid chemicals, watch and observe - you'll see the pond change daily!
 
Joined
Dec 16, 2017
Messages
9,757
Reaction score
7,708
Location
Ct
Showcase(s):
1
Hardiness Zone
6b
Country
United States
That handful looks like locus blooms. If you have that much getting in the pond and your only cleaning the filter once a week that can be a issue right there.
A skimmer with a foam pad is a prefilter and is designed to skim debris off the surface but it is not what i call a filter .
 
Ad

Advertisements

Joined
Jun 13, 2022
Messages
3
Reaction score
2
Country
United States
A skimmer with a foam pad is a prefilter and is designed to skim debris off the surface but it is not what i call a filter .

Fair! What sort of filtration do you recommend? I’m used to large tank systems having UV, protein skimmer, filter socks/pads, bioball compartment, etc. From poking through forums it seems like people generally put way less filtration on ponds, so definitely curious to learn if that’s true/what people generally find works best.
 
Joined
Oct 4, 2019
Messages
768
Reaction score
547
Location
Winchester, VA
Hardiness Zone
6b
Country
United States
Not necessarily less filtration for a pond, just different types.

Many here have bogs and highly recommend them.

I'm in a different camp and have a large bead type filter filled with K1 media. The water goes from that to a shower filter at the top of the waterfall, then back to the pond.

I do think you need a lot more filtration, the more the better in my opinion. There are plenty of options and no hard and fast rules as to what is best. You just need to find what works well for you and your pond. So research them all and find what you prefer.
 

netvine

Neophyte
Joined
Feb 27, 2022
Messages
77
Reaction score
61
Location
Humboldt Bay
Hardiness Zone
9b
Country
United States
Fair! What sort of filtration do you recommend? I’m used to large tank systems having UV, protein skimmer, filter socks/pads, bioball compartment, etc. From poking through forums it seems like people generally put way less filtration on ponds, so definitely curious to learn if that’s true/what people generally find works best.
on a sidenote for informational purposes: A shortcut to other option you may want to look into... the Sand and Gravel filters, sometimes called "S&G" that are typically made from 55 gallon drums. These I've read can replace the mechanical and bio filters people spend thousands on.a good search term for this is "birdman sand and gravel filter".This seems to me to be the general consensus on the best dollar for dollar koi filter. But folks on here have proven to me at least that a properly installed bog filter is just as good, and prettier! if you have the space. Also, Koi keepers have had a lot of luck with anoxic filtration systems, especially in the uk.
 
Ad

Advertisements


Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments. After that, you can post your question and our members will help you out.

Ask a Question

Top