# Alum to clear a pond



## [email protected] (Dec 22, 2006)

I've been researching using Aluminum sulfate to clear ponds and I think I'm going to try it. With feeding this year and little rain my pond isn't as clear as it was in past years both from planktonic algae and suspended clay from runoff in the nearby fields. Here's an interesting article
http://www.minneapolisparks.org/default.asp?PageID=832

I found the dosage is 60lbs per acre foot for moderate. For my pond that works out to 220lbs. It will lower the PH so my plan is to add about 40% hydrated lime immediately after spraying a slurry of the alum mixed with water over the ponds surface to bring the PH back up.

The other option was gypsum. Gypsum was more readily available but was going to be more costly and a more work than I wanted to do moving literally a ton of the stuff.

Here's my calculations. Anybody have any thoughts on ups and down of doing this?

11'	Max depth
7.333333	Avg depth
21780	Sq. Ft. (1/2 acre)
159720	Cu. Ft. water
159.72	
12	Rate Gypsum per 1000 cu. ft.
1916.64	Pounds Gypsum needed
0.1	Cost Gypsum per pound
$191.66	Cost to treat with Gypsum
Results in 1 to 4 weeks	
1916.64	Total pounds to distrubute


3.666666	Acre feet
60	Lbs Alum per acre foot
220	Pounds Alum needed
0.65	Cost Alum per pound
143	Cost Alum
40%	Ratio Hydrated lime to balance PH
88	Pounds Hydrated lime
0.1	Cost lime per pound
8.8	Cost Lime
$151.80	Total Cost to treat with alum
Results in a few hours to a week	
231	Total pounds to distrubute


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## Fishman (Apr 5, 2004)

If it's really bothering you go for it, but unless you have a serious sediment issue I wouldn't spend the money on it. If I understand correctly the treatments basically only last until it gets stirred back up again. The photos you've posted always look like you had a heavy plankton bloom

The Ph issue, how badly do you expect it to rise with the Aluminum sulfate application? There's a product called PhosClear that ya use at 80# per acre foot. It's buffered and doesn't mess up the Ph so bad you need to apply something else to correct it. Total price is damn near double though.

If ya trust you're numbers go for it  Make sure ya post results before and after shots would be really appreciated... never actually saw someone do this on a large scale.


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## [email protected] (Dec 22, 2006)

My bloom is a little stronger than ideal right now. Not dangerous yet but my pond is low and the nutrients are concentrated. I'm hoping that in addition to clearing the pond, the alum will bind up some phosphates to slow down the filamentous algae in the spring too. The alum treatments last upwards of 15 years according to the article and what settles out should not become resuspended. Incoming water with suspended clay is another issue. I ordered 200 lbs. of alum that should be in this week. I'll do my best to document it and post whether it works or not.


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## Fishman (Apr 5, 2004)

Looking forward to seeing this from an educational point of view, thanks


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## [email protected] (Dec 22, 2006)

I'll applied 200lbs of Alum this weekend. Visability was 7" and pH was 7.4 when I started around 10:30 AM. I mixed the aluminum sulfate with water in a rubbermaid tub then used a 2" electric trash pump to spray the slurry evenly over the pond. 
Here's a picture off the end of my dock. There is a clay tile 13" under the surface that you can't see.









This is the pump and mixing tub

















Here's the alum at work, binding up solids in the water (floc)

















Here we are a couple of hours after the application started, the tile is now becoming visible. ph was 7.2.









30hrs later my visability was 20". pH still holding at 7.2


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## Fishman (Apr 5, 2004)

Wow! Incredible you can actually see the flocculents forming! Thanks for sharing!


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## [email protected] (Dec 22, 2006)

Last night, some of the floc was still floating just below the surface. Hopefully it sinks with the rain in the forecast. I used a fairly low dose and it got my clarity back to a comfortable range but some literature says it may continue to clear. More alum would surely have made it clearer as well as cleared it faster but I'm not trying to turn it into a swimming pool. I ended up not needing the hydrated lime but anyone who tries this should have it on hand should the pH drop below 6.5.

The alum was a little less than I expected, $.55 per pound and I didn't need the lime so it cost less than $120 to treat my 1/2 acre pond.


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## Fishman (Apr 5, 2004)

Not to shabby at all, glad to hear the pH didn't become an issue, really didn't think it would. Did it ever budge from 7.2?


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## [email protected] (Dec 22, 2006)

No, it stayed at 7.2. I read somewhere that it works better the higher the pH is. 

The floating floc finally sank. Visability looks like it's still around 18"-20"

The pictures don't do it much justice. The difference is more obvious in person. The fish seem unaffected and are still feeding the same. I thought they may eat more pellets since they can see them better but that really doesn't seem to be the case...it's hard to account for the weather variable though.


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## Fishman (Apr 5, 2004)

Very cool man, make sure to let us know if you get any delayed settling. I thought ya said it, but I can't seem to find it, what was your clarity before the application?


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## [email protected] (Dec 22, 2006)

Visability started at 7 inches and ended up at 20 inches. I have no doubt that putting more alum in would clear it more.


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## Fishman (Apr 5, 2004)

Very nice! Thanks again for sharing


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