Pond Boss Forums GENERAL QUESTIONS Muddy water alum

I began adding alum to my lake according to the recommended rate; however, nothing happened other than a 8.7 to 8.5 pH drop. So I continued to add more every few days or so [in hopes of it clearing], but still no clearing--just a 8.5 to 8.2 pH drop and now milky/cloudy water. Did I put too much or not enough? I performed slurry tests and the alum works excellent in the jar, but not in the lake. Any suggestions before I continue to add more??? Thanks a whole lot.

What is your rec rate, I normally see the water quality look worse after application as the acidic effect on the bottom is so great that it burns off matrial for a short period of time and often appears as a brown film or scum, This is when alum is used in the granular form. Did you just add granular or make a solution first, are you circulating the water of letting mother nature do it??What material are you trying to drop to the bottom ??

Alum produces water clarity by aluminum precipitation as ALOH and trapping solids with the very voluminous floc that is formed. Minimum aluminum salt solubility occurs at 6.5-6.8 pH. until you get to that pH, the alum you added will stay somewhat soluble. Depending on the water, I would not think that more than 20-30 ppm as alum would be needed, but the pH will need to be lower to get the precipitation you need to clear the water. As respiration takes place this spring (when water warms and pond life resumes in full flurry), the pH will begin to swing with CO2 solubility. This may result in the needed lowering of the pH and a clearing of the water.
Can you calculate he volume of the water in the pond and the addition of the alum to get a close approximation of the addition rate? If less than 10 ppm, then morte may be needed. If more than 30 ppm, maybe you need to wait.

I've used alum and gypsum to clear ponds. Alum is actually a more difficult job and if it works it may not last as long as gypsum.

I can get gypsum in bulk at low cost, then use a boat and a water pump to disperse it. Because it raises hardness, there are added benefits to pond productivity.

In summary, if you are looking for a more long-term solution I would recommend gypsum in bulk.

Very good fact sheet from SRAC which I hope people with turbidity questions (cloudy water) will read. Then they will understand the problem and the solutions.

http://srac.tamu.edu/tmppdfs/13452410-46...45b52c83d6ee864


"Although not nearly as effective as alum, gypsum also can be used to control turbidity but without the loss of alkalinity. Gypsum must be added to achieve a concentration of 100 to 300 mg/L for effective turbidity control. For most ponds, gypsum application rates will range from about 1,000 to 2,000 pounds per acre (Fig. 4). In hard-water ponds (calcium hardness greater than 50 mg/L), the water is nearly saturated with calcium and gypsum may be ineffective. In that situation, alum will be the only effective coagulant."

In my experience, 90%+ of ponds with 50mg/l or higher hardness will not have turbidity problems unless there is a physical disturbance issue.

Listo, if you are in East-Central Texas, your water hardness is probably less than 50mg/liter.

We discussed mechanical turbidity vs. chemical turbidity at the conference. I'm assuming gypsum and alum could help in either situation, but it seems like the "fix" would be extremely temporary with a mechanical disturbance issue as opposed to a chemical disturbance issue...unless the mechanical problem itself is corrected. Does anyone have experience with gypsum helping at all in mechanical disturbance situations? If so, for how long?

I heard them discussing the mechanical vs. chemical turbidity issue and did not understand their distinction. With many years of water chemistry background, I had never heard these terms used, unless they are referring to mechanical means of generating the turbidity vs. water chemistry facilitating the turbidity.

Basically, turbidity as measured, is simple light scatter across a light measuring device. In clear water, there is no light absorption or scatter, so 100% of the light source is measured at the photometer ad zero turbidity is seen. Solids and color both add to measured turbidity so you relly do not know what is cuasing the "turbidity" . Solids have a net negative charge, and if they are small enough in size will be dispersed in the water column, with settling rates influenced by the water chemistry (impact on charge density).

Removing small suspended solids can be accomplished by coagulation (increase in solids size by reducing negative charge, allowing small particles to grow into larger size that settle faster) and flocculation (addition of a flocculating substance that "glues" the particles together into very large, fast settling solids). Adding Alum, gypsum, ferric sulfate, ferric chlorides, or any number of commercial organic coagulants (or a combination of any of the above) works to cancel the negative charge on the solid surface, as well as precitate the solids as a hydroxide floc. Alum works best around 6.5-7.0 pH due to aluminum having the lowest solubility at that pH. AlSO4 robs OH from H2O to create the ALOH, and lowers pH in the process. If you do not have enough alkalinity in the water, then a little Alum will drop pH drastically before you get enough soluble AL in the water to do you any good. Gypsum (CaSO4) does the same thing, but dissociates to form CaOH floc. The impact of gypsum on pH depression is not as drastic, but the solubility of CaSO4 in water is limited, so the addition rate can be significantly more. As Todd mentioned, gypsum use rate can be 200 lb. per acre foot, vs. 60-100 with Alum. Ferric salts can be used, and in the Midwest where steel production is found, can be obtained as a waste pickling liquor for practically nothing. Ferric works great (either sulfate or chloride), but is more difficult to handle (is an acidic liquid).

If you have enough alkalinity in the water use of alum is recommended due to lower feed rates and easier to disperse as a quickly dissolving powder. If you do not have high enough buffering, then you may need to add lime to counter pH depression, making gypsum a preferred method (single addition product, less chance of pH depression).

You can determine feed rates and effectiveness of each with jar tests using the mason jar technique. This is recommended. If you want to determine the buffering content of your water (changes based on chemistry) you can do a back titration method to determine PKa values. (if you are interested in a complete water chemistry session, let me know and I will give you the synoptic version of 25 years in this business).
Mike

Hi Mike,

Your assumption was correct. They are speaking of turbidity caused by either mechanical means (wave action, fish disturbances) or chemcial means (the actual chemistry of the water facilitating the turbidity/suspended solids).

It's interesting to me how the vernacular of differing discplines can cause confusion. I guess this is analagous to people in the south calling flathead catfish mudcat or yellow cat, but people in the midwest call bullhead catfish mudcat and yellow cat. Hence, scientific names are available as a common thread to alleviate confusion.

The old tried and true method we fish heads use to determine the cause of turbidity is the mason jar techinque. Take a sample of water and place it undisturbed somewhere for about a week. If the water remains cloudy, then it is at least chemical, but if it settles then it is mechanical.

I am glad you posted. I was able to add to my knnowledge bank, especially with regards to the ferric compounds.

Hey Mike,

I have fairly severe charge-induced turbidity. I plan to patiently add alum in small quantities until I notice a very slight clearing over 2-3 days. I believe that by adding alum until you get a drastic overnight clearing, that you are adding substantially more than you need. For every pound of alum I add, I will add several pounds of lime. Does my plan sound reasonable?

Bobad,
Yes, although you may not need to add any lime at all. Try the jar test method. Calculate the amount of alum you want to add, add that amount to a 1 quart mason jar ( approximately 1000ml.), shake to dissolve and disperse, then let set and see what happens. If you start to form a " pin floc" about the size of a pencil tip, gentle stirring may actually cause these to grow and settle quicker. After settling, check the pH. If you are below 6.0 and you got good clarity, then you may have added more than you need. If not, and more does the trick, again check the pH. If you add to much, then solubility starts to increase as pH drops below 6.0 and you may have to add lime to raise pH and drop the added aluminum and solids out of solution.

One additional note. There are other forms of aluminum salts that are used to clarify waters. Poly-aluminum chloride (PAC) and Aluminum chlorhydrate (ACH) are both liquid versions of aluminum salts. They work the same way as alum, but are easier to feed (liquid vs. solid). In the case of PAC, some long chain polymer impact of the aluminum is seen, and sometimes works better. The only down side is they cost approximately 2X alum.

One last thing. In my experience, no more than 10-30 ppm of alum or PAC is usually needed to clear up surface waters. I would start at 10 ppm and work up.

Thanks Mike. Good info!