Pond Boss Forums GENERAL QUESTIONS Water chemistry Concern about water chemistry in my pond

While my HBG are feeding well, I did water testing today and have concerns that something may be going badly. This is a 2 yr old, .3 acre aerated pond that averages 8' depth with deep sections to 12'. Testing results follow :

pH = 6.2
total alkalinity = 40
total hardness = below 50

I feel that all these readings are low and need to be raised. What's the best way to accomplish this? I'm planning on adding YP and HSB later this spring and want water quality to be able to support them.

My guess, add 600# of ag lime.

Is this a spring or groundwater pond (water source)?

If not then adding some ag lime will help (500 lbs). Your test results are ok but could be better. 20 on alkalinity is minimum for a productive pond while 200 is ideal for pond fish.

Bagged ag lime (not hydrated lime).

Ewest, this pond was well-water filled and maintained.

Then you need to manage the water to keep it up to needed conditions. Was the well water tested the same ? If so then adding some lime will help.

Lowe's sells a pulverized limestone by Soil Doctor that was about $3.13/40lb for 10+ bags...less magnesium content, but iirc, 1400# equal 1 ton of Ag Lime, so a bit higher in CCE.

Adding 400# pelleted ag lime in the morning. I'll see what the chemistry is like in a few days. TSC is selling 40# bags for $3.00 / bag.

Thus far I've added a half ton of pelletized lime. Took new readings today and have seen some improvement in water quality.

pH before 6.2 after 7.2
total alkalinity before 40 after 40
total hardness before below 50 after 150

While pH and total hardness are much better, total alkalinity hasn't moved. Any suggestions?

Wait a month. Takes some time for lime to work its magic.

I know, snrub. It's only been a week. I was just surprised that the pH and total hardness showed significant improvement but nothing on the total alkalinity.

Pelletized lime takes a little more time than ag lime to work.

I'm hoping one of the experts jumps in to explain why the pH and total hardness jumped up but not the total alkalinity. There has to be more to it than pelletized ag lime takes more time.

Lets see if I can explain and simplify this. Alkalinity and hardness are related but measured differently. Alkalinity measures dissolved carbonates and bicarbonates. Carbonates and bicarbonates are electrically charged and change back and forth due to different living activities (mostly from plants) going on in the water. Carbonates buffer or 'mediate' the pH and tend to keep it more stable. The amount of buffering capacity depends the amount of carbonates dissolved in the water. Limestone (lime) is mostly calcium carbonate.

When you add lime to the water the calcium carbonate separates into carbonate and calcium. Hardness tests measure two of the main minerals dissolved in water - calcium and magnesium. NOTE: Dolomite has calcium and some magnesium carbonates in the reference above by ewest. Limestone is mostly Calcium carbonate.

This is what I think happened in your situation. When you added lime, it dissolved and separated into calcium and carbonate. Then something in the pond absorbed or precipitated the carbonates removing them from the dissolved form or condition. This left the calcium still dissolved and it was measured by the hardness test. New added carbonates were no longer dissolved and were not increased.

Thanks for that explanation, Bill. It now makes sense. So, do I need to add more lime? Adding that half ton about did me in

Larry,
How are you generating your water ph, alkalinity, and hardness info?
Taking samples in to a lab? Or do you have your own monitor? If so, what monitor are you using?
Thanks,
Jeff

Jeff, I'm using simple 5 test, test strips. They're available most anywhere that sells pool supplies.

Thanks. I've used them before. I was just curious if an inexpensive accurate monitor was available. My pond isn't quite three yrs old. The guy I spoke with at the Missouri Dept of Conservation told me I probably didn't need to be too concerned about water quality for a few years. I'm not sure if that's exactly the case, but so far it seems healthy.

Larry - I think that if you add more lime to make whatever is absorbing the carbonates to become saturated then the alkalinity will begin to increase. If I were doing it, I would first do this as a test in 5 to 10 gallons of pond water to see how much lime(teaspoons or tablespoons) is needed to increase the alkalinity. There 16 level tablespoons per cup, one cup weighs about 0.5 pound.

When successful extrapolate or expand this amount to your pond volume. If plant activity is causing the carbonate binding then you may have to add more lime than the calculation. But I think the test addition of lime in a smaller volume of water will give you a good idea of where to start as a beginning amount.

When adding lime to your pond do you "Have" to spread it out everywhere or can you dump it on say one shore line? I can get lime to my pond but no way can I get it all over the pond. Will it still help?

Can you dump it in a flowing inlet creek or no?

Sorry no hijack intended here just thought it may go along with the discussion.

thx,

RC

It is best to somewhat spread ag lime out over the pond bottom. It will still work if you only spread it out in a few places but not as well or efficiently. Keep in mind you are treating the cause of the low alkalinity (the dirt) as well as the effect on the water.

IMO in most cases spreading the lime out in an upstream inlet or the dry watershed is not a wise use unless there are no other options.
A spreader truck backed up in several locations around the pond is the best way absent a boat/barge application. When I get the spreader truck to come I have them dump a small % on shore for me to put out in the pond by boat.

Bill's test idea is a good one. To best replicate the effect on the pond put about 1 inch of pond dirt compacted on the 5 gal bucket bottom and allow the turbidity to settle. Then add the lime and test.

Advanced reading about hardness and alkalinity.
Alkalinity can be defined as a measure of waters capacity to neutralize acids. Alkalinity is caused by weak salts of acids. Technically there are 3 primary forms of alkalinity 1. carbonates, 2. bicarbonates and 3. hydroxides. Alkalinity inter-reacts aggressively with carbon dioxide to cause changes of bicarbonate to carbonate and carbonate back to bicarbonate. However when alkalinity is measured it usually tests for the combined amount of carbonate & bicarbonate.

Other things that contribute to hardness are strontium, ferrous iron, manganous ions and sometimes aluminum and ferric ions in dissolved solution. Hardness is caused primarily by the soil and rock formations. Hardness to the layman is the soap consuming capacity or amount of soap required to form a foam. Limestone formations are a big cause of water hardness. Some of the difficulty of understanding hardness is possibly due to there is a carbonate and non-carbonate hardness or aka temporary hardness.

In waters with lots of calcium, calcium carbonate (lime) is precipitated.

Suggest you read these from SARC on water quality.

https://srac.tamu.edu/serveFactSheet/112 -- Alkalinity , ph. , hardness and CO2


https://srac.tamu.edu/serveFactSheet/262 -- Water quality interpretation

Thanks ewest, they were very informative.

Bill, I'm using pelletized lime, so I'm not sure how that test would work. I guess I could get a bag of ag lime to do the test with and extrapolate the results. I'll be in town tomorrow and pick some up to do the test. Thanks for your input.

One trick on pelletized lime. Most pelletized lime has a coating. I earlier said it takes longer than ag lime to effect the water (not the dirt). This is because it will , if just dumped in, fall to the bottom quickly and work on the dirt. With ag lime some dissolves on contact with the water so you see an immediate effect. The trick is to wet the pelletized lime in a bucket for a couple mins before you pour it into the pond. You get a quicker short term effect than if you just dump it in.. Long term is the same for ag lime and pelletized (more or less).