Tom, thanks for the advice. I realized after I had already posted that the daily 10% water changes were probably more excessive than I intended. Some details on my tank can be found in this thread: Big Project
Pics are on page two of that page. It's got two circulation loops. One that runs 2 sumps and another that just circulates water from the center of the tank through a carbon canister and back to a drilled T-Pipe that runs along the bottom rear of the tank. I'm planning on removing the carbon canister from the second loop and using that loop as my injection point for ferts and CO2.
theredben: I'd already thought about the nutrient inconsistency of the river water. To make matters more interesting, we have 8 sewer plants upstream from us who all dump their treated water back into the river.
Whatever I do I will end up doing a lot of water testing. I'm planning computer control of all the automation. Will probably end up using an adjusted PPS-pro method, and may separate NO3 and PO4 into individual solutions so I can control their dosing independent of other nutrients.
I wish there was an electronic way to test of NO3 and PO4... That would make life a little easier. :P
One other little fact that I Just remember that is probably relevant: There was an article in the local paper recently about our city water system and one of the things that they mentioned was that the water department had been adding ammonia to the water to stop corrosion or something, but they stopped doing that because there were too many complaints about the smell.
As far as automation and testing, this requires a lot more work and details and management than you might think.
There is no automation for NO3/PO4.
So that's manual testing and is a PITA, if you plan on using the data for any dosing, you will have to calibrate the test and make sure they are correct, just like using a pH meter and a 2 point reference with 4 and 7 pH's.
So you will need a a set of reference solutions for the NO3, I'd not even worry about PO4 testing unless you plan on using strict PPS, in that case, you'll end up with a lot of GSA on the glass and plants, and at 500 gallons, that will be a PITA.
So modify the dosing for 3ppm for PO3 and about 20ppm for NO3 as targets.
These will float and move around so here or there, but as long as they are in those general regions +/- 40% or so, things will be fine.
CO2 is far more important and will be a MUCH larger issue, EI/PPS, they both add the same things, one is richer, the other is hold over from PMDD days and leaner.
So adding more of one is the same as adding less of another.
How you get there does not matter to much.
If you want to adjust the dosing, you can use water changes, easy, fast, no testing or uncertainly there.
Or you can use test kits and adjust according the those and do less/few water changes, that is the trade off. PMDD suggested this as have I in the past. EI evolved from PMDD and PPS is almost identical to PMDD and while not cited, obviously took nearly all other than the PO4 limitation part for the dosing method. Not like I have not done both for long time.
There is no magical method that avoids both test and water changes and still keeps the dosing the same.
Adding enriched sediments would be close to that, but even there, you still have to dose. A non CO2 method would be as close to the no test, no water change methods, but it seems you like CO2/techy stuff, so I'll assume that is your goal.
I'd avoid the mythical fully automated everything, that's justr askign for systems failure and more work in the long run.
More nick nack to go wrong, dump in way too much nutrients all at once, pH probe breaks, falls out, kills the tank etc. Simple, hard to break, and good routine maintenance will go much farther.
Also, while you might have a lot of motivation right now, testing gets really old really fast. I have more experience testing water than most ever would like to say they have. Few hobbyist with 5-10 years of experience bother testing week to week, few even month to month, most do not after a bit.
Folks nag you to test but often do not do it themselves.
The tanks I do have not been tested, some have for a time by their owners, they always stop after a time though and realize it's not required once they get some experience, know what to look for and watch their tanks and do not neglect them.
Dosing is only a small part of this, CO2 and light is 90% of it. You sound like the light is in good shape, so most of the issue now will be CO2 and mixing.
Seal the sumps up(duct tape the dry sections so that no air/gas can exchange) and raise the overflows so they only drop about 2", add a hofner grugle buster(search google etc) to each.
This will eliminate most of the CO2 loss from the sumps.
I'd just feed the CO2 into the return pumps or use a fine stone to feed them to reduce the impeller noise as the CO2 hits.
Unlike many folks, I have a long historty with large tanks in this size and a few orders larger. Management is not the same as simply using nutrients to magically solve all your problems, many imply that, it's simply not the case.
You must look at the big picture.
Otherwise you end up with a huge mess, lots of labor and time spent on the tank and the cost goes way up then. I'm glad you have the light you do on this tank, that's one saving grace.
CO2/current will be your nemesis, nutrients will be easy.
I'd suggest you read Left C thread on CO2 dual stage regulators and get the best CO2 reg, needle valve and solenoid you can. I have used mass flow controllers from Alicat, CO2 meters from Oxyguard etc.
These are 1200$ and 3000$ each.
I do not think those are practical here, but a good reg, good needle valve (Nupro 's SS 1/8" with a vernier caliper handle makes adjustments incrementally far easier).
Just go slow and methodical with CO2, do not get impatient, do not adjust and then wander off for the rest of the day, watch the tank closely when you adjust the CO2. Do not get gun shy with CO2 either if you go too far.
Good current will save you and make it much easier to manage without any issues.
Good plant selection and scaping will also make the result look much nicer and easier to care for. Chose plants that are easy to grow and grow on wood etc.
Amano did this for his large tank, as did I with the tank above and with this tank:
This client suffered since the sediment is plants and it's 4ft deep.
But, he does not bother testing or spends much time on dosing, he has a hard plumbed tank so drain and refill is easy. Water is cheap, testing and labor is not.
All he does is turn a valve to drain(10 minutes), and then shuts it off and turns another to refill. Since the tank is deep, you have to drain it down to get in and work on it.
He does a water change about once every 2 weeks, sometimes longer now.
So the water change is perhaps the easiest part, and it does not cost more than shower or two extra a week's worth of water. That's 1$ at the highest water prices in CA which are some of the highest in the USA for this 1600 gallon. Since it's hard plumbed, it also involved no labor or testing.
He also suffered due to high light disease (HDL). Now the tank is light limited, around 25-30 micromol at the bottom. You tell these folks what to do, but they think they know it all. So you let them suffer till they give up and try it your way.
This is my version at the 60 gal scale:
Very easy to care for, I change the water 2x a month, never test, these fish have been in here for 3 years now.