Phosphate in mixed salt

[neiltus]

I have had high PO4 on my tank, up to 1ppm. It's a 75g Reefer with TBS rock. Levels got up to 1ppm via Hanna and Salifert. I change about 15g of water a week, sometimes more trying to combat this.

I recently started running GFO for about 2 months. I also changed salt mix at the end of this period, mostly because I wanted to use a non-reef salt that was a little less expensive and there were some decent sales on it. My PO4 dropped with what I thought was judicious use of GFO, often changing it every few days to bring that 1ppm down to about .03-.09. My hammer, nems and other corals looked better. I also started dripping Kalk saturate during this period.

When I started using GFO, I was having a dino outbreak as well. I vacuumed the crap out of the sandbed and blew off rocks during the 2 months of GFO use and did some large water changes with the new salt. The dinos thinned.

Two weeks ago I opened an older box (my last) of reef salt that was in the garage. I threw away the box, mixed up 17.5g for a WC. My PO4 went up from .04 to .09, I changed GFO and put 3tbsp of BRS HD GFO, not wanting to drive PO4 to nil. Last Saturday I did a 17.5g WC. On monday my PO4 was .24 via Hanna and then confirmed with the Salifert test at .25~

Today I mixed up 4 gallons of the reef salt to put in a QT tank with a pair of wrasses. I thought I would test those 4 gallons for PO4.

Hanna

Salifert

Well crap, something must be wrong with my RO.
Hanna RO

Anyway, the salt I am using is HW Marinemix, the salt I changed to because it was on sale was Red Sea Blue.

I wish I still had the HW box, as I tossed it after I rolled the bag to put it in the empty red sea container.

As far as controls, I have not directly mixed salts in this storage container. The salt in the bag is HW. The bucket I used was a 5g HD bucket that is wiped with vinegar and air dried after use so I don't accidentally cross contaminate tanks with QT water.

I know Hanna has a .03 margin of error, but when I look at my salifert test I see close to .1, I don't have a direct white balance on the photos.

I assume HW allows a measurable amount of PO4 in the reef salt to allow for corals and if someone is carbon dosing.

Seems this is one clue to my PO4 problems, using a reef salt when it's not really needed due to a new tank.

Thoughts?

 

[Griff500]

The level of phosphate in your water change shouldn't be an issue when you take dilution into account. Apparently feeding is going to introduce far more phosphate.

 

[bertoni]

I agree that the level you show for the change level is too low to cause the phosphate problem that you're seeing, although I'm surprised there's any detectable phosphate. The Hanna is only good up to ±0.04 ppm + 4%, so that reading is acceptable. The Salifert indicates some phosphate is present, though.

I agree that food is the most likely source of the problem, although some live rock arrives contaminated with phosphate that it then leaches into the system. Some GFO might be able to solve the problem, although it can get pricey if there's a large reservoir of phosphate in the system. I'd give it a shot, and consider switching when the price seems to be getting a bit high. Lanthanum chloride is a lot cheaper to dose, although more tedious to use.

 

[neiltus]

My actual DT currently is testing under .05 for phosphate. It was much higher till I ran GFO, did water changes and vac the sandbed. I have had a LOT of die off on this rock.

Fish load/feeding load is minimal. I added my first two fish-small Potter's Angel and a Yellow Prawn Goby. I would target feed the shrimp in the system.

I assume die off and the leaching theory contributed to the PO4 more than the salt did.

Appreciate the input guys.

 

[bertoni]

Ah, I see. Well, you could run some GFO on the change water, but it's sad to have to do that.