Acros struggling after Po4 spike

[Rick's Reefing Adventures]

Hey everyone,

Looking for some advice. I have a 25g acro-dominant tank and recently had a massive bryopsis outbreak. After manually removing as much as possible, I treated the tank with Flux.

As per instructions, I removed carbon and turned off UV during treatment.

The good news: the bryopsis is almost completely gone.
The bad news: about 50% of my acros are now doing poorly.

Observations:
- Polyp extension is actually great
- But I’m seeing dead spots and dead tips on several colonies
- Some of the dead areas are already starting to collect algae

I ran tests and noticed my PO4 jumped from 0.08 → 0.202 ppm since the treatment started.

My guess is the dying bryopsis released nutrients and spiked phosphate.

Current situation:
- No carbon (removed for Flux treatment)
- UV off
- No phosphate-removal media on hand right now
- Algae mostly gone

Questions:
1. What’s the best move right now to save the acros?
2. Should I frag/cut off the dead tips to prevent algae from taking over?
3. Should I do a water change, even though the Flux instructions say to wait another week?
4. Any other immediate steps you’d recommend to stabilize things?

I’ve attached some pictures of the affected acros.

Appreciate any advice — really don’t want to lose these acro’s.

 

[LobsterOfJustice]

How has your alk been during all this?

 

[Rick's Reefing Adventures]

How has your alk been during all this?

I test once a week and sadly didn’t think about testing more during this… last few weeks was: 7.5, 7.5, 7.8, 7.4. I dose all for reef and adjust it when needed.

 

[Roatan Reef]

I test once a week and sadly didn’t think about testing more during this… last few weeks was: 7.5, 7.5, 7.8, 7.4. I dose all for reef and adjust it when needed.

You might need to raise your alk, that seems kind of low for Acros.

 

[dvgyfresh]

Did you do a big water change after the reef flux?

 

[Rick's Reefing Adventures]

You might need to raise your alk, that seems kind of low for Acros.

Really? I thought anything above 7?

Did you do a big water change after the reef flux?

I did not, the instructions say no waterchanges for 14 days, its been 7.

 

[dvgyfresh]

Really? I thought anything above 7?


I did not, the instructions say no waterchanges for 14 days, its been 7.

Ok up to you , I’ve stopped treatment short of I notice most algae is gone and see inhabitants struggling - the dead algae creates a lot of DOC and increases phosphate / nitrate and if not immediately removed after it dies will make it grow back

 

[Rick's Reefing Adventures]

Ok up to you , I’ve stopped treatment short of I notice most algae is gone and see inhabitants struggling - the dead algae creates a lot of DOC and increases phosphate / nitrate and if not immediately removed after it dies will make it grow back

Thanks! I’ll do some waterchanges the next few days to lower phosphates. I still have some algae that I’m removing daily, but the phosphates don’t help in this case. Do you think I should cut the dead tips or let it be?

 

[dvgyfresh]

Thanks! I’ll do some waterchanges the next few days to lower phosphates. I still have some algae that I’m removing daily, but the phosphates don’t help in this case. Do you think I should cut the dead tips or let it be?

I don’t really do acros just nems , maybe #r#reefsquadould be of more help

 

[P-Dub]

Hey everyone,

Looking for some advice. I have a 25g acro-dominant tank and recently had a massive bryopsis outbreak. After manually removing as much as possible, I treated the tank with Flux.

As per instructions, I removed carbon and turned off UV during treatment.

The good news: the bryopsis is almost completely gone.
The bad news: about 50% of my acros are now doing poorly.

Observations:
- Polyp extension is actually great
- But I’m seeing dead spots and dead tips on several colonies
- Some of the dead areas are already starting to collect algae

I ran tests and noticed my PO4 jumped from 0.08 → 0.202 ppm since the treatment started.

My guess is the dying bryopsis released nutrients and spiked phosphate.

Current situation:
- No carbon (removed for Flux treatment)
- UV off
- No phosphate-removal media on hand right now
- Algae mostly gone

Questions:
1. What’s the best move right now to save the acros?
2. Should I frag/cut off the dead tips to prevent algae from taking over?
3. Should I do a water change, even though the Flux instructions say to wait another week?
4. Any other immediate steps you’d recommend to stabilize things?

I’ve attached some pictures of the affected acros.

Appreciate any advice — really don’t want to lose these acro’s.

Okay, it sounds like you’ve got a bit of a conundrum. The advice I’m about to give may differ somewhat from what others suggest.
I definitely feel your pain with Bryopsis. I went through a pretty severe outbreak myself and followed the standard fluconazole treatment protocols with excellent results. That said, based on what I can see in your photos, the Acropora generally look okay—but the images aren’t clear enough to make a truly accurate assessment.
I do agree that your alkalinity is on the low side. Starting the treatment at around 8–9 dKH likely would have been preferable. I always ran my alkalinity toward the upper end of the range, around 10–11 dKH. I do not necessarily recommend you do the same. At this point, however, I don’t think making alkalinity adjustments will have much positive impact on already stressed corals. In fact, changing parameters while they’re compromised could potentially make things worse.
I also ran GFO in a reactor to address the expected phosphate increase and manually removed bryopsis aggressively throughout the treatment.
At this stage, it’s honestly a gamble whether to continue and finish the treatment schedule or to stop and allow the system to stabilize, hoping the bryopsis has been sufficiently weakened or eliminated. Either option has risks.
If it were me, I would stop the treatment, continue regular water changes, manually remove any remaining algae, and let the tank stabilize. If the bryopsis returns, I’d prepare more thoroughly for a second treatment. That would include having ample GFO and a reactor on hand, using it judiciously, and testing phosphate and nitrate daily to monitor effectiveness and determine when media changes or inclusions are needed. I’d also start with a slightly higher—but still reasonable—alkalinity, have pre-mixed, stabilized saltwater ready for use, and purchase more fluconazole than I think I’ll need to account for any dilution from needed water changes, GFO use, or skimmer use. Use these only as absolutely necessary, and then replace any Fluconazole removed from these to keep levels effective. You're going to have to estimate.
This treatment can have significant consequences, and there doesn’t seem to be a clear consensus on which conditions or parameters contribute to negative outcomes. In my case, treating a heavily stocked, acro-dominant mixed reef went very smoothly—but I was prepared for most contingencies and followed conventional guidance closely. I may also have simply gotten lucky.
You don’t necessarily need to cut the tips unless algae begins accumulating on them, and the tank has stabilized with the Acros clearly improving. As an alternative, you can cap affected tips with a small amount of underwater two-part epoxy and allow the coral to grow over it.
I’d really like to see clearer photos of the affected Acropora under normal daylight or using a color-correcting filter. Also, keep in mind that the issues you’re seeing may not be directly related to the fluconazole treatment at all.
Either way, keep us posted.

 

[Mr. Mojo Rising]

Ok up to you , I’ve stopped treatment short of I notice most algae is gone and see inhabitants struggling - the dead algae creates a lot of DOC and increases phosphate / nitrate and if not immediately removed after it dies will make it grow back

Agree 1000%

 

[LobsterOfJustice]

Mid 7's is fine for acros, it's where I keep my tank. It's good your numbers are stable, but in general I think you should be testing alkalinity more than once a week if you're serious about keeping acros.

I agree that overall the acros in the pics look okay. I understand the reef flux directions want you to wait another week for a w/c, but personally, if anything is looking off in the tank, especially during a treatment, I would just do a w/c. You kind of have to just go with your gut. You can always repeat the treatment again later.

 

[P-Dub]

Mid 7's is fine for acros, it's where I keep my tank. It's good your numbers are stable, but in general I think you should be testing alkalinity more than once a week if you're serious about keeping acros.

I agree that overall the acros in the pics look okay. I understand the reef flux directions want you to wait another week for a w/c, but personally, if anything is looking off in the tank, especially during a treatment, I would just do a w/c. You kind of have to just go with your gut. You can always repeat the treatment again later.

Let me explain a bit more why I feel your alkalinity may be on the low side, even though I agree that around 7 dKH can absolutely work in some systems. As @LobsterOfJustice pointed out, that level is fine for his tank, and there are plenty of successful reefs running there. My point IS NOT that 7 dKH is inherently wrong, but that it sits close to the lower edge of the usable range, which leaves a smaller margin for error depending on how the system is managed.

On the other end of the spectrum, I also recognize that the 10–11 dKH range I ran is on the high side, which is why I don’t generally recommend either extreme as a default target. For me, it really comes down to risk management and safety margin. When alkalinity is already low, it doesn’t take much of an unrecognized consumption spike, dosing interruption, or testing gap for levels to fall into a range where pH stability and calcification can become an issue. The same concept applies on the high end, just with different risks.

In my case, the system was heavily stocked with a very high calcification demand. Even running a calcium reactor with multiple chambers, including magnesium, it still wasn’t enough to maintain the growth and coloration I wanted. I ended up supplementing with two‑part to keep up. Because of that demand, running alkalinity on the higher side actually reduced my risk of an unintended drop. I also had the benefit of tight control with an Apex managing dosing with a DOS, and frequent automated alkalinity testing with a Trident, which significantly changes what ranges are reasonable and safe.

With lower alkalinity targets, especially if testing isn’t frequent, the margin for error is simply smaller. I don’t know your exact calcium and alkalinity demand or how often you’re testing, so I’m looking at this from a conservative standpoint based on what I can infer from your system and husbandry. That’s why I suggested something like 8–9 dKH in your case. It provides a bit more buffer against unnoticed fluctuations without pushing into what most would consider the “high” range.

This approach isn’t uncommon at all, and many reefers land there for exactly this reason. At the end of the day, it really comes down to what level of risk you’re comfortable with and how tightly your system is monitored. Looking at the tank holistically and planning for the inevitable bumps along the way is what usually makes the difference long‑term.

Just my 2 pennies worth...

 

[CHSUB]

Dieing algae release all kinds of stuff, including metals it uses for growth. Do a WC immediately and get back to regular maintenance…

 

[mfollen]

Agreed
You can always administer another dose. The main thing is to remove what compounds are in the water. So long as your water change water is relatively stable alkalinity wise.
Best of luck