API Phosphate Test Accuracy

[SaltyBuddha]

Just getting into SW. Have had FW tanks for a long time and I've been using the API test kits. Currently curing some dry rock and it's been about 3 weeks. I didn't test the first few weeks because I figured it would be pointless. Now that I am testing for phosphates, I cannot for the life of me tell what color the solution is. The cards color scheme is so close together it is really hard to tell. I'm using it for FW since I'm curing in dechlorinates tap water. The SW card looks a little better though.

 

Anyone else have this issue with the phosphate test kit? At this point I will probably just start cycling this weekend and deal with any more phosphate leaching at that time.

[SaltyBuddha]

Tested the curing water against the tap water and it looks like there are some phosphates still leaching. At about .5 ppm after 16 hours. Much easier to tell the difference with a control. Good thing my tap water is phosphate free 

[seabass]

The API phosphate kit is a high range kit, which goes up in 0.25 ppm increments.  And like you say, it can even be difficult to determine the difference between 0.0 and 0.25.  However, the target range for a reef tank is typically 0.01 to 0.03 ppm.  Therefore, that test kit isn't very helpful in achieving the target range.

 

At a minimum, I would suggest a Salifert phosphate kit.  The colors are still a little difficult to determine, and it goes from 0.00 to 0.03 ppm.  When using this test kit, I look for the slightest tinge of blue.  And if I have trouble telling if it's 0.03 or 0.1, then the phosphate level is too high.  It should match, or be lighter than 0.03 (while still having a slight blue tint).

 

I mostly use the Hanna ULR Phosphorus Checker.  It has a digital read out which eliminates the hassle of comparing the sample to a color chart.  It also goes up in increments of 1 ppb (that's parts per billion).  The target range of phosphorus is 3 to 10 ppb.

 

If the phosphate, which is being produced by your rock, is coming from organics which are breaking down, then (after the organics have broken down) it will eventually stop adding additional phosphate into your water, and water changes can remove it.  However, if the phosphate is coming from the rock itself, this can cause an ongoing battle with phosphate (and algae).

[SaltyBuddha]

3 hours ago, seabass said:

The API phosphate kit is a high range kit, which goes up in 0.25 ppm increments.  And like you say, it can even be difficult to determine the difference between 0.0 and 0.25.  However, the target range for a reef tank is typically 0.01 to 0.03 ppm.  Therefore, that test kit isn't very helpful in achieving the target range.

 

At a minimum, I would suggest a Salifert phosphate kit.  The colors are still a little difficult to determine, and it goes from 0.00 to 0.03 ppm.  When using this test kit, I look for the slightest tinge of blue.  And if I have trouble telling if it's 0.03 or 0.1, then the phosphate level is too high.  It should match, or be lighter than 0.03 (while still having a slight blue tint).

 

I mostly use the Hanna ULR Phosphorus Checker.  It has a digital read out which eliminates the hassle of comparing the sample to a color chart.  It also goes up in increments of 1 ppb (that's parts per billion).  The target range of phosphorus is 3 to 10 ppb.

 

If the phosphate, which is being produced by your rock, is coming from organics which are breaking down, then (after the organics have broken down) it will eventually stop adding additional phosphate into your water, and water changes can remove it.  However, if the phosphate is coming from the rock itself, this can cause an ongoing battle with phosphate (and algae).

Thanks for the suggestions on better test kits. I'll definitely look into them. And yeah, the rocks are still in the curing stage but I'm expecting them to stop leaching phosphates in another week or two. 

 

Thanks again for the suggestions!

[Clown79]

Salifert test kit is much better, more accurate, and low range.

 

By the time you see results with api, phos is already too high.

[SaltyBuddha]

6 hours ago, Clown79 said:

Salifert test kit is much better, more accurate, and low range.

 

By the time you see results with api, phos is already too high.

Didn't know phosphates needed to be that low. I've done more research on it now though. Idk why API makes the test that high then.

 

I'm going to invest in another phosphate test so I know when the rocks are fully cured 

[Clown79]

You want phos at 0.03

 

I'm not really sure why they make it that way either. 

[seabass]

1 hour ago, SaltyBuddha said:

Idk why API makes the test that high then.

The API phosphate test kit is really geared for freshwater aquariums.  Planted freshwater tanks do well when phosphate is between 0.25 and 0.5 ppm, and tend to experience problems when phosphate approaches 2 ppm.  The API phosphate test kit works fairly well to monitor phosphate in these ranges.  However, while this same test kit works in saltwater, it's just not an appropriate range for a reef tank.

[SaltyBuddha]

Yeah that makes perfect sense for freshwater. They should have a separate test for their "reef" master kit though lol 

 

Thanks for all the input guys. Can't wait for these rocks to cure so I can bump start the cycle

[seabass]

2 minutes ago, SaltyBuddha said:

They should have a separate test for their "reef" master kit though

I couldn't agree with you more.  That phosphate kit should never be included in anything targeted for reef tanks.  They'd be better off not including a phosphate test kit at all.  I wish they'd market it as a high range kit, so that people use it properly.

 

I think it's harder to develop an accurate kit for the low ranges targeted for reef tanks.  And while I would think that API could develop an acceptable low range kit, it's probably not something which they feel will yield a good return on investment.