Zero Phosphate

[5Bucks]

3 months ago my tank turned 1yr and I had an algae problem. I had monitored PO4 with Hanna tests at the LFS once a month. In the first 9 months they ranged from 1.6 to .06. NO2 and NO3 have always been very close to zero. With a relatively busy summer I missed testing for a couple months. I still kept up with bi-weekly 10 - 20% water changes but it was not enough. PO4 test in late October showed 2.36 and I had a lot of algae growing. So I started an aggressive PO4 reduction program. Perhaps too aggressive as a few days ago PO4 was zero. I've been told I must have some PO4 for the corals unless I go ultra-low nutrient and start dosing amino acids. LFS says their SPS stock displays are usually .04 - .08. I've always heard .06 or below is good. LFS says they tend toward .08 to more closely match average customers levels.


I'm not sure how my levels got so high. I had been keeping up on water changes with RO water from LFS and if anything was feeding less. Two months ago I purchased an RO/DI system. No more paying for water and lugging buckets! My suspicion is the RO from LFS wasn't exactly perfect. If that's the case it's no longer an issue. Maybe I was feeding to much, but I hadn't really changed the amounts. If anything was feeding less leading up to the huge PO4 number.


At this point, I guess I'm happy that I was able to reduce the PO4. Even if I went to far. Algae is gone except for a little on a couple of base rocks I couldn't remove and scrub. Emerald crabs and other cleanup crew are slowly removing what's left. Went from cleaning glass almost daily to every 4 or 5 days. Corals including Duncans, Zoas, Slimer, leather and a couple of small sps frags seem to be doing fine but I'm concerned that won't be the case long term if PO4 stayed at zero. So what's a good way to get PO4 to more reasonable levels? I know nothing about ULNS (ZEOvit?). Is it reasonable to attempt in a system with fish? I'm assuming I can just feed more and cut back on PO4 removal methods to get levels up.


Here's my plan. Any feedback is appreciated:
1. Feed more.


2. Carbon dosing reduction. Slowly taper off the booze. I worked up to 1.5mL/day on 65 gal. system volume over the past couple months. Going to cut this back by 5% each week for next 4 weeks and evaluate further reduction.


3. Reduce my DIY GFO reactor flow/add no new GFO to reactor. It's currently running at approx. 90gal/hr. Going to cut flow to 60gal/hr.


4. Macro algae: I added some to the sump 2 months ago. It quickly doubled in mass first few weeks - when PO4 was high and has not grown since. Still looks healthy so I'm just going to leave it in place.


5. Algae scrubber: Going to leave this in place. It's grown just a very little since I installed my DIY unit 3 months ago. I never had a good pump to feed this so the flow is very slow maybe 10 gal./hr. I've never had too clean it off.


As I start to get more into SPS corals I'm focused on keeping the system stable and making no drastic changes.


Other parameters:
65gal total system volume
dKH averages 7.5 - 8.5 w/manual drip dosing of 1/2 tsp. soda ash/day
pH: don't test often but always 8.2 or 8.3 when I do
NO2/NO3: test once a month and always zero or very near
Salinity: 1.026
Calcium: Been running kind of high as much as 520 a month ago now at 460-480. LFS says not to worry and attributes to doubling up water changes (20% weekly) with Instant Ocean Reef Crystals when I first started on PO4 reduction. I have not dosed calcium for about 2.5 months.

 

[Randy Holmes-Farley Verified Community Expert]

Letting phosphate rise is generally quite easy since every feeding adds a lot of phosphate. I'd be wary of doing too many things to boost it as that will likely send it higher than you want.

Reducing the flow and/or amount of GFO sounds like a good plan to start, and you can always do the others later if needed.

 

[5Bucks]

So just took another look at recommendations for PO4 level for reef aquaria.
Is .03 or under what I should be shooting for? Should I stop worrying/testing and let growth on the glass direct my control efforts?

I'm thinking it's a darn fine line between between .00 and .03.

 

[Mercurio]

I would advise against letting your phosphate get to .00. I had this happen a few months ago due to running an different brand of GFO than I normally do. Needless to say I had a MASSIVE outbreak of dinoflagellates that wiped out my entire tank of SPS. Another reefer in my club also had the same thing happen to him so I know I'm not alone. Only the zoas and some of the LPS survived. I think .03 is a fair number to shoot for.

Edit: Forgot to mention that I used a Hannah Meter to check Phosphates.

 

[Nano sapiens]

Some tanks run '0' testable phosphate and everything thrives, some run elevated levels and everything thrives. This is what confuses people the most. Remember that when you test for phosphate you are only testing PO4 (aka 'Inorganic Phosphate' or 'Orthophosphate'). There are other phosphate species that we don't test for due to the costly/complicated equipment required and that these species can be converted to PO4, and visa versa, in an aquarium so you can see that it's a moving target, of sorts, and the different forms of phosphate may be in different ratios in some tanks vs. others.

Testing is fine and maintaining a level of 0.03 or so works for many tanks. Personally, I test for PO4 very rarely since I nearly always get a '0' reading (Salifert). I rely more on the coral color and algal films that develop on the aquarium walls. Roughly, if coral color is good and the walls develop a light, but visible algae film every 3-4 days , then I'm 'in the ballpark' and need not worry

 

[Randy Holmes-Farley Verified Community Expert]

The target you want to pick for phosphate may vary depending on what's in the tank and whether there are any existing pest issues, but 0.03 ppm is usually good for a mixed tank.