Here is where things start getting interesting.
10/15 I do a round of testing:
pH: 8.2
Alk: 8.1
Nitrate: 32.1
Phosphate: 0.0
All tested using Hanna kits
pH 8.2 / Alk 8.1 dKH prefect for coralline and bacterial balance
Nitrate 32.1 ppm Right where it should be. That’s still residual from the ammonia dosing and the start of the bloom collapse. fine for fueling coralline and biofilm growth. This should drift down slowly through normal bacterial and skimmer activity.
Phosphate 0.00 ppm This the red flag. I've probably hit a temporary phosphate crash because the phyto bloom and early film bacteria pulled nearly all available PO4 out of the water. Also running ozone with the skimmer can amplify that.
So I need to reintroduce trace phosphate, just enough to bring it back into the measurable range (0.02–0.05 ppm).
I'm a big fan of mixing your own dosing solution (as you will find out) . I have some monopotassium phosphate that I will use to make up a dosing solution. For my tank I have about 330 gallon, or 1250 Liters. If you are going to start dosing on you own I recommend thinking in liters not gallons. it makes things much easier. So for 1250 liters I need to mix 10g of monopotassium phosphate (MKP) into 1 Liter of rodi water. That gives me a solution of 0.00227g PO4/mL.
(monopotassium phosphate, MKP)
So each mL of this solution adds ≈ 0.00227g
For my system I get these dosing guidelines
+0.01 ppm = 5.5 mL
+0.02 ppm = 11 mL
+0.03 ppm = 16 mL
So I will start with adding 11ml to a high flow section of the sump to dose the tank. This also gives me a slight potassium bump, a little less than 2 ppm of K, which is fine. It's good for coralline and SPS.
So on 10/16 I dose 11ml MKP. The next day, skimmer is running very good and pulling some really dark skimmate. I just cleaned the cup 15 hours ago, so a good amount of skimmate, exactly what I wanted. I test P on 10/17 and it is at 0.01 awesome. So that tells me that the tanks daily phosphate demand is roughly 0.01–0.015 ppm/day right now. The idea is to not let phosphate bottom out, tons of things are using it in a new tank. Bacteria, diatoms, and coralline are using phosphate to grow, also dry rock and sand (because they are new) will absorb P until they are saturated. Once that adsorption layer saturates, P will stop disappearing so fast and that’s when I can start to see coralline spread and film algae balance out. So I add another 10ml of MKP on 10/17 as well.
10/18 P is at 0.02 on the Hanna meter. AND the sand looks marginally better of dinos, and the water column definitely looks clearer of phytoplankton, still cloudy but I can see progress. Looks like the skimmer and ozone are helping with the bloom and the higher P hopefully keeps the dino at bay. So no MKP dose today and I will test again tomorrow.
(phytoplakto bloom is lessening)
(sandbed is looking better too)
10/19 P is again at 0.0 on the Hanna. So Phosphate demand is still in force. So I dose another 11ml of MKP. No other changes.
So I've been a fan if higher N and P for a very long time. With my old tank 10+ years ago I was dosing nitrates and monitoring phosphates to keep them stable. At that time my tank was already established and phosphates were more of something to monitor so they don't get too high. But in a new tank, phosphate disappearing isn’t algae using it up, it’s the system not being finished yet. Fresh rock, sand, and media chemically bind phosphate, and early bacterial biofilms consume huge amounts of it while the tank is building its biological foundation. Until those surfaces and microbes are saturated, any P you add just vanishes and read zero. So right now I'm testing and dosing phosphate so the tank can reach an equilibrium, that's the point where the tank stops instantly absorbing everything and starts biologically cycling nutrients. Once that happens, phosphate becomes stable and more predictable instead of always falling back to zero, then the system can behave like a more mature reef instead of a nutrient sink.
10/20 phosphate tested 0.00. So the tank’s still soaking up P. Yesterday’s +0.02 ppm went to 0 in 24 h so the surfaces/biofilm aren’t saturated yet. This time I will dose 0.03ppm and split it between the morning (11ml) and the evening (5.5ml). 10/21 Still testing 0 phosphates. I do the split dosing of 0.03ppm of MKP. Next day 10/22 I get 0.05 on the Hanna. Hopefully the system is stabilizing. The Phytoplankton bloom is looking much better too, funny how adding phosphates can help the tank overcome algae problems.
(Phyto bloom is significantly less, alright)
OK so now I have a dilemma. I have been monitoring phosphates so closely and I have to leave town on 10/23 for a few days to go to a wedding. I don't want to make a mistake with all I have been doing. I can have someone dose the tank but they can not test anything. So I measured P right before I leave for my flight on 10/23, Hanna measured 0.02 PO4, good. I will dilute 6ml of stock MKP into a 475ml jar and leave that for my friend to add on 10/25 in the evening while I am away. I feel that 6ml is still probably safe, with the drop overnight, and diluting it in a jar makes it easier for the person just to dump it into sump rather than slowly adding 6ml from a small vial.
So those are the instruction, I go off to my cousins wedding, have an awesome time. I come on 10/26 and test my Phosphates...0.06ppm. I love it when things go according to plan.