Will post pictures soon. We have a 1 surface acre/8 acre feet pond that we have filled up with well water. Here in central Texas, we had a hellova spring with the rain and we got a lot of runoff which caused colloidal clay/iron buildup in our pond. We have no fish in the pond
Visibility was about 2 inches. Our alkalinity was about 240, pH of 8.2. We dumped in 200 gallons of 70% sulfuric and 1500 lbs of alum and dropped our pH 1 pt and got it to clear to about 18 inches visibility.
We're putting in another 1200 lbs today and that should finish it off and completely coagulate any suspended particles.
As we pump it out for irrigation and replace it with well water, will we lose the charge holding together the clay on the bottom? Will it only re suspend if it is turbid? The bottom of the pond is about 30 feet so it will be a challenge for anything to stir that up. (outside our diffuser). If so, any recommendations on how to remove all the crap on the bottom? Giant pool vaccuum?
Jonnn, your pH of 8.2 is completely fine! I wouldn't use the acid at all! Does your hardness nearly mirror your alkalinity? Did you do a "jar test" to see if the clay settled, so you know if alum was even needed?
The sulphuric acid probably reduced the Alum's ability to flocculate. Alum itself is acidic, and should be offset with 50% by alum weight of caustic Hydrated Lime, another positively charged ion.
The positively charged Aluminum Sulfate will attract and hold the negatively charged colloidal cay particles and sink to the bottom. Unless vacuumed out, it will remain on the bottom to help resettle the captured clay quickly, if it gets remixed into the water. However, if more colloidal clay enters the water through runoff, the magnetic field of the Alum can be overwhelmed, and more alum needed.
The fluffy floc (crap) on the bottom, will compact over time to less than 1/4" of thickness.
The flocked colloidal clay will never resuspend, but the alum originally used may not be able to remove NEW colloidal clay entering your pond.
My use for the sulfuric was to lower the alkalinity. The alkalinity acts as a buffer against the alum working. It should have been neutralized instantly before adding the alum.
Our pond has been muddy since day 1 and never settled.
So as I replace this lower pH, lower alkalinity water with a higher alkalinity water, it won't lose its charge? Good to know.
Here's the before and after. Turns out I only needed 350 more lbs of alum.
My use for the sulfuric was to lower the alkalinity. The alkalinity acts as a buffer against the alum working. It should have been neutralized instantly before adding the alum.
Our pond has been muddy since day 1 and never settled.
So as I replace this lower pH, lower alkalinity water with a higher alkalinity water, it won't lose its charge? Good to know.
Here's the before and after. Turns out I only needed 350 more lbs of alum.
I'm not sure what you mean about your alkalinity acting as a buffer against the Alum.....that higher pH is what helped alum work. The acid hampered flocculation.
A buffer (Hydrated Lime...Calcium Hydroxide)...Is always recommended, especially when fish are present. Too much acidity will allow aluminum to dissolve into water, and also reduces the floc rate.
I'd say you were lucky you had not stocked fish yet, or most would likely have died from pH shock, but regardless, the final result looks good!
The higher the Alkalinity, the more Alum you have to add. A local pond guy told me I need to add acre feet x alkalinity in terms of lbs of alum to be in the ballpark of what I needed. I ended up using about 260 lbs per acre foot ballpark.. So he was pretty close. I would think 260 lbs per acre foot is considered high in your experience?
The Alum is acidic when in contact with water and soluble. When in contact with water you get Al2(SO4)3+6H2O--->2Al(OH)3+3H2SO4 The H2S04 is sulfuric acid. The free large particle of aluminum bonds quick with the colloidal structure of clay making a large heavy compound. The acid is then left to fend for its self in the water solution. This is why it is recommended to add some positively charged calcium hydroxide to make calcium sulphate and H20.
With out the calcium hydroxide like Rain man said you could end up with a low PH. Adding more acid like you did allows for better use of your Alum because its not trying to bond right quick with your waters high alkalinity trying to tie up the Aluminum. This gave the Aluminum time to react with the clay then the soluble alkalinity.
The higher the Alkalinity, the more Alum you have to add. A local pond guy told me I need to add acre feet x alkalinity in terms of lbs of alum to be in the ballpark of what I needed. I ended up using about 260 lbs per acre foot ballpark.. So he was pretty close. I would think 260 lbs per acre foot is considered high in your experience?
I didn't add the lime because I have no fish.
I typically apply 200-250 pounds of alum per acre-foot of water, and estimate "high" on "average depths" for calculating water volume. 200 to 225 pounds of Alum would have probably worked had the sulfuric acid not been added. I disagree with your "pond guy". When I have used Alum/Lime in water with a pH of 6.5 or lower, I end up using nearly double the dose before the flocculation began. Ph of 7-8, an "average dose"...above 8pH, floc occurs much sooner.
High alkalinity COULD mean you would need less Hydrated Lime only. The Hydrated Lime is a buffer against the acidic Alum. Higher alkalinity in the pond has "built-in" buffering, but the risk of pH shock killing fish due to a rapid pH drop is higher. Obviously, with no fish, you did not have to be concerned with that risk.
I'll take donoBBB chemical equations as accurate, I'm not a chemist, but I do know low pH slows the Alum from creating a floc, and extra amounts are needed than in waters with a higher ph, so I can't agree the acid "helped".
Adding the Hydrated lime, even without fish or to buffer the pH drop is still a good thing. the Hydrated Lime adds additional positively charged Ions to attract the negatively charged colloidal clay. While there are definite chemical reactions occurring, I am not sure the magnetically attracted clay being drawn to the aluminum molecules is one...
See clay and soil is considered a cation compound meaning it is negatively charged. Aluminum is positively charged +3 so its looking to stick to the negatively charge. Being such a large molecule they make up large heavy flocks that sink or titrate out.
I can see what your saying Rain man that if the acid content is to high the bond between the aluminum and sulphide may not want to break in the first place in the water solution. The water having so many negatively charge particles all ready.
The extra flock you see Rain man may be from the fact that the hydrated lime is freeing up extra positively charged calcium +2 and water when mixed with water. This then is tying up more negatively charged clay.
EDIT: you can then tie up more clay quicker with out having a PH shock from just using alum.
I do agree that to much acid could have effected fish I am no expert with that but I do know that the larges strongest chemical bond would have won the battle.
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