10 ppm PO4 - need help

Saltyxxx

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Yes, you read that right. I've been struggling with po4 issues for a while now, and recently I have realised that my test kit might be malfunctioning - now I think that my po4 is way, way higher than what I believed it to be, and I am at a loss of what to do.

I keep a 100 gallon 3 ft saltwater tank, and though I mainly keep a fowlr system, I have been trying for a while to grow corals, starting with frags of the easy beginner soft corals. However, it has been a recurring trend that corals I add into my tank will grow quickly at first, then their growth will stall and some eventually just give up and die altogether. I've chalked it up to my lack of experience / skills since I am still a beginner to this hobby, but eventually I did get to a point in the last 6 months where my corals could grow quite happily and my zoas were multiplying like crazy, and so I thought I was doing better in this department.

However, over the last month all the soft corals in my system have been exhibiting signs of stress - polyps not fully opened and not growing well, and all of my zoas have this distinctive umbrella-shaped appearance that I know is a sign of stress but am unsure of how to troubleshoot. I'm currently having issues with green film algae in my tank, but I clean the rockscape and glass regularly, especially near the corals, to keep them free of overgrowth. I used to have issues with green hair algae, diatoms and cyano, but they have all cleared up over time and now my tank is free of them. I have 8 fish in my system - 2 clownfish, 2 wrasses, a tailspot blenny, a firefish, a royal gramma and a coral beauty. I also have a bunch of nassarius snails on cleanup. I feed 2x frozen food and 1x pellet each day, and I don't feed anything more than what my fish won't eat after 30 seconds.

Now this whole time, I've been using the salifert test kits to track all of my water chemistry parameters - PO4, NO3, Ca, Mg, KH and pH - and test every 2 weeks. Most of my parameters are within a normal range, as seen from my latest results:
25 ppm NO3
450 ppm Ca
1320 ppm Mg
11 dKH
pH 8.3

The one parameter that has always been a problem spot for me is PO4, which consistently comes in at 0.1 to 0.25 ppm (from as early as the days when my tank was brand new and still cycling), and I know the ideal should be 0.05 ppm or less. The main treatment I've been using is that I've been dosing red sea NOPOX daily, as well as running bacteria treatments weekly (either brightwell aquatics microbacter clean or dr tim's waste away), in addition of course to a chaeto refugium and a reef octopus classic 110-INT protein skimmer. I do a 25% water change once a month, but I do sometimes get lazy and skip a month here and there. My PO4 values didn't budge despite all I was doing, but I wasn't too stressed about it, since my algae issues were in check and my corals were doing fine and growing quite well up until about last month.

Some time around last month, all of my corals (mainly soft corals) suddenly started to show signs of stress - which as I mentioned earlier, had to do with polyps not opening, or zoas showing an umbrella shape and having elongated necks. I tested all of my values and they were more or less the same, so I was perplexed. I started to suspect that maybe there was something wrong with my test kits, especially because my PO4 values in particular have remained so consistent despite my corals obviously reacting to something that has changed about the water.

The reason that I suspected this is also because, around 3 months ago, I ran out of reagent for my po4 test kit and had to buy a new one. Within the same week of switching to a new kit, my PO4 values - which had been stable for >1 year at 0.1 ppm - jumped up suddenly to 0.25 ppm. I was shocked, but since I was already running treatments for nitrate and phosphate reduction, I focused on how my system as a whole was doing, whether there were sudden algal blooms or corals were showing issues (which they weren't back then). But looking back now, I realise this might have been a warning sign that the test kits I was using were faulty.

So with this in mind, I went out to my LFS yesterday to buy two more phosphate test kits, one by Colombo and one by API, both of which are stated to be suitable for saltwater systems. I tested the same batch of aquarium water on all 3 kits within 5 minutes of each other (photo below). The API kit showed 10 ppm phosphate - the highest possible value on their scale. The Colombo test kit, which has an upper limit of 0.8 ppm, corroborated this because the colour was so dark and intense it exceeded the scale, so safe to say it is way higher than the salifert value of 0.25 ppm. I read the instructions for all 3 of these kits very carefully and performed them exactly as the manual stated, and ran the Colombo kit 2 times and API test 3 times in the same day just to make sure that I wasn't doing anything wrong.

Side note: As a precaution, I checked the expiry dates on all my phosphate test kits and all of them are well over a year away from their stated expiry date. I am also aware that salifert test kits come with a warning that they aren't accurate if there are extreme values of dKH in the system (>20 dKH), but as shown in my parameters above, my dKH has never exceeded 12 and I always keep it within the safe and healthy range of 10 to 12.

Here's the photo showing the results from all 3 kits. For reference, API is at the top, Colombo on the left and Salifert on the right. Again, these tests were conducted within 5-10 minutes of each other from the same batch of aquarium saltwater.
1661578551701.png


I am now quite convinced that the po4 salifert test kit is faulty and that my aquarium's PO4 values are way out of whack - though I'm not sure how much to trust the values given by the other kits as well. I'm currently running seachem phosbond to specifically treat for these ridiculously high PO4 values, but honestly I feel like it is too little too late - this must have been a problem this entire time and I've been scratching my head as to what the issue is, and turns out that I was using a faulty test kit that has totally misled me. Any advice on what I can do - a larger water change maybe?
 

DE FISH

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I'd trust the results from the Salifert kit over the other two. Have you asked your LFS to test your water?
I agree with the above. I don’t trust my eyes with po4 tests so always use a ulr hanna checker.
 

Uncle99

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Those kits cannot read below .25ppm accurately.
Fell into the same stuff your experiencing.

The only device that gave me accurate readings on phosphate was the Hanna UL Phosphorus Checker which is in PPB.

My previous tests always showed no lower than .25ppm even if I ran GFO continuous.

I tried the Hanna Checker that tests for phosphorus in PPB and found I had been running at zero (the GFO). This kit always gave me more believable numbers and twice ICP and the test kit variance was just 5PPB!

So I pulled the GFO, dosed up my phosphate to .07ppm or 23 PPB and one month later, DT back thriving again.

The test for trace amounts of phosphate is difficult because there’s so little of it in our water chemistry.

In addition, I have found the Hanna Alk and HR nitrate to be just a reliable and super fast.
 

taricha

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One kit is older, and was unresponsive to changes made in the tank.
Two other kits are new and agree that PO4 is off-scale high. I agree with them.
I don't know how PO4 binders work at such high concentrations so I'd do water changes before PO4 binders.
 

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