I forgot to mention a couple of things earlier. Just came in from measuring the system and got a CF=23 so I guess I have to confess that the earlier estimate was a guess and it was a little off.
Yesterday I topped off the system with water and mixed up a gallon of nutrient concentrate. You do that rather easily by mixing 17 ounces of white mixture into a gallon of water, and then 17 ounces of the blue mixture into a gallon of water. That makes two gallons, one of white and one of blue, concentrate. The general rule is one ounce of concentrate makes one gallon of nutrient (that's one ounce of each mixed into the gallon of water ... you can't mix the concentrates at full strength because then chemical reactions take place that precipitate out some of the nutrients, but when they are mixed at the delivery strength they don't react. Don't ask me, I'm a physicist not a chemist, apparently there is a concentration requirement.). Anyway I'm not sure how much water is in the pond because I didn't measure it, just added nutrient until I got the readings I was looking for. A quarter cup of concentrate moves the CF in the pond about 2 points.
At some point it will be a good idea to pump the nutrient over the side and maybe use the old nutrient to fertilize the garden and refresh the nutrient in the pond. The reason for that is that the nutrient is balanced for tomato plants but there is no guarantee that it will stay in balance and our instruments are too crude to tell since we only look at overall ion concentration. So every month or so it is a good idea to empty the pond and replace it with fresh nutrient.
There is some build up of algae in the pond, but not very much since most of it is not directly exposed to sunlight. All in all it's going well. The CF (Conductivity Factor) instrument I'm using is the truncheon which was developed in New Zealand. It works very well and I think they have skyrocketed in price to about $130.00. When I bought mine it was less than $100. I have two because I couldn't resist seeing what the new one was like. Turned out to be not too much different from the old one, just a little prettier. They are both working just fine.