Hardness and alkalinity both in mid to upper thirties. I've dumped a lot of lime over the years, but it's a never ending battle.
Dump a BUNCH more in. I'd want to see it in the mid 40's before I'd consider putting in any fertilizer. We are a good 100 points higher than you are and do nothing to the water.
Frank, Given you have seen some very strong blooms in the past ... both planktonic and BPW ... these water quality parameter seem to be limiting factors. You may have plenty of nitrogen and phosphorus but just need to right chemistry to mobilize these nutrients.
I completely agree with your last statement. When the PH of a water sample flips it will flip really fast. When you have all these nutrients available but not tied up with another covalent bond they can just flip in minutes.
If you can use calcium carbonate as much as possible the material will act like a buffer. It will bond with free nutrients and try to keep the PH at 7.2 as best as it can. Only calcium carbonate has this ability to do this.
Now from my back ground in chemistry ammonia sulfate based fertilizers are very alkaline but when added to soil tend to go acidic because plants really like the ammonia and not the sulfur. This leaves the sulfur free in the solution to become acidic. If you had free calcium carbonate kicking around this would absorb the extra sulfur making calcium sulfate and tie it up again out of the solution.
At some point one will have enough calcium carbonate that the PH will stay and fix at 7.2 and will not move no matter what fertilizer is added. At this PH most of the needed fertilizer is readily available for plants and errors on the safe side. A lower PH say 6.5 will be best for water fertilizer but can be hard to keep from growing out of control.
Just my thoughts and view. Cheers Don.
