N and P are the two main reasonable/plausible nutrients to test for. K+ test kits are rarely made, two companies make them and they are too broad ranged to be much use. K+ can be dosed without worry of nusiance algae blooms using K2SO4. I will not get into the issues surrounding Fe test kits for bioavailability here. It's too much and too long often.
NO3 test kits are notoriusly inaccurate when measured up against standards in the the range many SW/FW folks with plants/macrophytes need. Generally 0-10ppm is a good working range but I've only found the Lamott or Hach test kits to give me and many other aquarist obsessed with testing plant/algae uptake rate with *reliable results worth interpting.
If you have the option, measure the NO3 uptake without a Refugium/Caulerpa etc over the course of a week.
Don't feed and then do a week with feeding fish/critters.
Then add the refugium and wait till it's fairly well established and repeat.
Some NO3 will be lost to the DBS etc, but the rest can be assumed as macro algae uptake. It's important to have a healthy growth rate established to compare a healthy stand agaist the rates of nutrient uptake.
A so so stand of macro's is not your goal nor what you want to grow.
NO3 is the largest % of biomass and the test is fairly straight forward with less issues of beyond the range of test limitations vs say PO4 limitation with macro's and other algae. You can see uptake by a good biomass of PO4.
But the NO3 is 10X-15X the amount per day.
A reasonable resolution for a Lamott test kit is 1, maybe 2ppm.
You'd have to go to a spectrophotometer to do much better. But you can measure 1-2ppm uptake rates over a day due to refugiums. 0.1-0.2ppmppm of so of PO4.
You assumed correctly that you ran out of nutrients and the Caulerpa stunted and died back. Adding small amounts of NO3/PO4 can help or switching the lighting to a more moderate intensity would help. Increased feeding may also be a simpler solution but I don't think that alone will help in this case due to the very large jump in lighting intensity. But this can be over done/has limits also and you'll get traces of NH3/NH4+ which can cause blooms of nusiance algae. Back to the issue of balance for the boiload.
It's a bit like driving a car, the faster you go, the more fuel you burn(Nutrients) and the more likely the chance of a crash will be more painful.
More light is not always better, _balance_ is what folks should perhaps seek, not bigger and more powerful.
But at higher light intensities you will see the uptake rates appear faster and change faster over time. Just don't run the plants/macro's too low and crash the tank.
I use KNO3 and KH2PO4. I do large water changes every two weeks as the tank is small but the other nutrients can be dosed if you do the water changes in smaller amounts/less frequently but it's tougher to maintain a good range of parameters.
The KNO3 will add a fair amount of both K+ and NO3 and the KH2PO4 adds the PO4. If you want to add namely K+, K2SO4 works well. These three will give complete control over the dosing of NPK.
These run a 3-6$ lb from
www.litemanu.com for perhaps a lifetime's supply.
I added up to 10-12ppm KNO3 per week to my tank but I have started feeding more and using about 1/3 of the KNO3 as it it provides strong growth without melting the Caulerpas from the exceed end of the range.
Too much or too little will cause issues.
0.0ppm of NO3/PO4 is not good for macro's.
I have not done enough with the Traces(iron is my proxy for the traces)+PO4+ NO3 all at the same time of different methods of dosing it.
I'm slowly getting there though. Takes time.
Right now I dose tp 87 liters of SW:
500mg of KNO3 1x a week
50mg of KH2PO4
5mls of traces
I dose each on different days and add the traces directly on to the macros slowly with a pipette(2-3minutes) without the current.
I feed the fish well.
Adding all of these at the same time and at higher dosages did not give me a good result with Caulerpas.
Hope this might help.
Regards,
Tom Barr
