Phosphate media

[mark]

So reading here even if you test zero for phosphate you still have them as test kits are not reliable.

If that being true, how does on determine when to change phosphate media?

[midgetwaiter]

I've been researching this for a while now to write some articles about it for a new company website. It's a complicated subject.

First thing you have to realize is that most of the phosphate tests out there don't measure total phosphate. They measure orthophosphate which is phosphate not bound up as part of an organic molecule. This is the phosphate we need to worry about for things like algae growth.

The problem is that if you are introducing organic phosphate through food or source water it does eventually break down. If this happens at close to the same rate as the algae is sucking up orthoposphate you'll never be able to measure it. Some algae species actually make an enzyme that breaks down organic phosphate called phosphatase. Sneaky bastards.

So the biggest problem with test kits is getting a measurement of total phosphate. The Merc kit marketed by Deltec apparently does this, I haven't tried it yet. The accepted laboratory method for testing total phosphate involves acidifying the sample with sulfuric acid and reducing it over heat by half to beak down the organics then testing for orthophosphate. This works pretty good even without the acid and is called the heat test by aquarium types. Take your sample, heat to 80C for 5 minutes and let cool then test.

One thing I have discovered by accident is that the nutrafin test kit uses the same reagents as specified by the laboratory standard. The instructions for the kit tell you to wait 2 minutes after adding the reagents to compare to the colour card. Because the method it uses only works in acidic conditions the first reagent is sulfuric acid. If you add that acid like normal and then wait 20 minutes before adding the other reagents the acid has broken down enough of the organics to get a decent result. It is consistent with the results of the heat test in my messing around but I don't know if I'd say it works perfectly or anything.

The second thing that is wrong with simple test kits is the precision. If you have an SPS tank and are trying to get max growth even small phosphate amounts can slow calcium uptake. Trying to tell the difference between .1ppm and .2ppm on a cheap test is a bugger. The aforementioned deltec kit uses a special black block to keep stray light from interfering or you can get an electronic colorimeter like the Hanna model that reads the sample for you. There's basically nothing that provides low rage precision that doesn't cost some pretty big bucks.

Getting rid of a phosphate problem is tougher, most important is eliminating it from your water supply. You need DI to do it, plain RO systems let quite a bit through. You are still adding a huge amount every time you feed so better skimming helps to get it out when it's organic and phosphate removers like GFO help after it breaks down. Base the switch out on whatever total phosphate test method you use.

I've always found in the past that my fuge did enough uptake to handle phosphate for me but lately I've been having more trouble with it. This is the primary reason I'm switching to RO/DI for all my tanks and starting Ultralith.

That's kind of condensed, when I get the new website running I'll send you a link.

[mark]

Looks like you have put some thought into this.

Understand the difficulties in measuring phosphates and as doesn't seem the media itself in indicating (such as with types of DI resins) that's why I'm wondering on a method to determine when to change the media.

Do people normally just change out based on time similar to if running carbon (~6 wks)?

[fkshiu]

Originally Posted by mark

Looks like you have put some thought into this.

Understand the difficulties in measuring phosphates and as doesn't seem the media itself in indicating (such as with types of DI resins) that's why I'm wondering on a method to determine when to change the media.

Do people normally just change out based on time similar to if running carbon (~6 wks)?

That's what I do. Through trial and error and careful observation of the tank I change my GFO out every 8 weeks and carbon every 2-3 weeks. Carbon actually saturates quite quickly and some people even advocate changing it on a weekly basis, but that's kinda annoying.

[plutoniumJoe]

When running both GFO and Carbon which do you pass the water through first?

[fkshiu]

I go: GFO --> Carbon simply because GFO fines can irritate my clams so I want the carbon to pick it up.

[midgetwaiter]

Originally Posted by mark

Looks like you have put some thought into this.

Understand the difficulties in measuring phosphates and as doesn't seem the media itself in indicating (such as with types of DI resins) that's why I'm wondering on a method to determine when to change the media.

Do people normally just change out based on time similar to if running carbon (~6 wks)?

You'd change it when your measurement starts going over your target level. There isn't going to be a standard schedule that works for everybody, it depends of your total phosphate additions and how much gets taken up by other mechanisms, etc.

I got in the habit of mixing a half recommended dose amount of GFO into my carbon so I only used one reactor. That mix got switched every 2 weeks.

[JOEL]

Hc gfo instructions
Change the gfo when phosphate levels rise or algae growth becomes visible.
I will give that a try.