Pond Boss Forums GENERAL QUESTIONS Water chemistry Low Alkalinity, Good pH - Add Lime?

I'm looking for some advice on what to do with our water, especially relating to whether to add ag lime or not. This is pretty urgent, because we recently stocked YP, but have had a steady trickle of YP dying. Any advice is appreciated.

Here's some background, and the water test results:
Our water had a slight green cast to it in March and April, but since has been clear and getting progressively clearer as the season progresses. No rooted vegetation (due to grass carp), but we do have increasing amounts of FA (I'd call it a "moderate" amount currently). We can now see a rock pile and a barrel that were placed in about 8-10' of water. I had our water chemistry tested at Penn State, and here are the results:

• Nitrate: 0.8 mg/L
• Phosphorus: <0.025 mg/L
• Total Dissolved Solids: 33 mg/L
• pH: 7.2 (Note: Water sampled at 10am)
• Total Alkalinity: 8 mg CaCO3/L
• Hardness as CaCO3: 17 mg/L
• Iron: <0.1 mg/L
• Manganese: 0.05 mg/L
• Aluminum: <0.03 mg/L
• Sulfate: 7.0 mg/L

Questions: Any thoughts on the water quality/chemistry? Should we add ag lime, and how much per acre, given that pH is fine but that total alkalinity is quite low (I think)? Penn State's guidelines say that our pond's manganese is high, so is that an issue for our fishery? If so, where could manganese come from (soil?), and how to reduce it?

See full thread on my pond's revamp if interested in more background info:
http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=506290

Drew, do you have any readings on dissolved oxygen levels, especially in early morning?

From a purely layman understanding, if you arent experiencing big swings in PH, I'm not sure adding more lime will benefit you much. 7.2 is optimal, but if you do multiple checks throughout the day and find it is climbing into the high 8s or 9s, then lime would be beneficial to buffer those swings.

What is the water source ? Do you have mine activity in the area ? Old mining operations often result in acid water runoff.

Ag lime will help with alkalinity but the source of the problem is more important.

anthropic,
I haven't bothered with getting a DO test kit yet, mostly because we don't have a dock or a boat, so I'm not sure how I'd sample water from the deep. I've assumed that we're okay on DO for now since we never saw fish kills before and we've taken more biomass out than we've stocked (removed 30 LMB, 129 BG, a 20 lb GC), though I really should start checking it to know for sure especially since we've started feeding pellets.

Eric,
The main water source is a stream coming off the mountain, which runs through deciduous (mostly maple and oak) forest. As far as I'm aware there were never any mines in our immediate watershed, though I know the creek a mile or so away (around the mountain) has water quality issues due to old coal mine runoff. We're not farmers, but from what I've heard, I believe farmers in this area have to add ag lime to fields before planting anything because the soil in the region is acidic, I think due to the area being dominated by deciduous forests and having clay soils.