phosphates

[sea student]

I have been battling algae for ages, yet my test kit always shows zero phosphates. The lowest level the kit would show is .25 ppm (mg/l), but it is a subtle color difference. I tried testing my tank water, my tapwater, and ro/di water and they all showed zero. Do I need a more sensitive test kit?
I have a 90 gallon and I feed one cube of frozen per day. I have to admit that until recently I didn't always rinse the food, but how much can that really add?
I do a 10-20% water change every other week and have an ASM-3 protein skimmer with great skimmate.
The tank is 5 years old, lots of LR, no substrate.

[Randy Holmes-Farley]

No, you do not need a more sensitive kit, you just need more phosphate export (or less import).

While the concentration can be very low, when you have a lot of algae (whether problem algae or intentionally grown macroalgae) the measured phosphate level is low because the algae is taking it up as fast as it arrives in the tank.

The goal in this case is to intercept it before the algae gets it, and so many types of phosphate export methods will eventually cause a decline in the algae by preventing the algae from getting what it needs. :)

[Randy Holmes-Farley]

These have more on how to export more phosphate:

Phosphate and the Reef Aquarium
http://reefkeeping.com/issues/2006-09/rhf/index.php

The “How To” Guide to Reef Aquarium Chemistry for Beginners,
Part 4: What Chemicals May Detrimentally Accumulate
http://reefkeeping.com/issues/2007-09/rhf/index.php

[rgrobe]

Randy is right, it is the export of phosphate that is important.

I had a similar problem for a while and tried testing with API and salifert tests always at zero. Don't trust the kits. I now use a Hanna low range phosphate meter that will test as low as 0.02 (at least that is as low as I can get my tank to go).

Having Randy's advice a while ago I might have concentrated on using acceptable methods to lower phosphate There were telltale signs that the phosphate was present despite the test results. Now that I have the meter though, I have found it to be useful.

[LISound]

I was battling GHA. it's finally starting to go away. i was able to knock it down really fast by introducing some cheato. but the cheato died for some reason and made things even worse.

Here's what i did.

I got a GFO reactor and started running that full time.
increased WC's to 1 every 4 days and did about 30% or more each time.

Picked out as much as possible all the time and the stuff i couldn't get is now turning white and dying.

it's taken me over a month to get to this point.

now the bigger problem was my rock. My rock was about 5 years old and finally absorbed as much PO4 as possible. the rock was great but after 5 years, if started leaching those phosphates back into the water, feeding more GHA.

this went on for a year in a 55 gallon tank and i just went through it with my 20.

now i will always run GFO and carbon on my system.

I also gave the really dirty rocks an acid bath. I've yet to add those back into the main system but their going back in within the next month--so ask me then if it had a big difference.

[LISound]

oh, and my tanks were BB too. with the lack of a DSB to help control NO3 and PO4, it's either get real good clean rock or run GFO and stay on top of WC's

[pjf]

If I’m reading Dr. Holmes-Farley’s articles correctly, I can export phosphate by raising the pH, causing calcium phosphate to precipitate, and skimming the resulting crystals.

To concurrently fight algae (bryopsis?) and precipitate calcium phosphate, I plan to raise both the pH and magnesium levels in my system using Kent Marine Kalkwasser Mix and Tech-M. My drip system is ready to go, my chaetomorpha is hungry, my GAC/GFO reactor has fresh media, and I’ve got my Tunze skimmer in the shop being refurbished and “tuned.”

What pH and magnesium levels should I aim for? Do salinity levels affect calcium phosphate precipitation?

[Randy Holmes-Farley]

If I’m reading Dr. Holmes-Farley’s articles correctly, I can export phosphate by raising the pH, causing calcium phosphate to precipitate, and skimming the resulting crystals.

If that happens much, it is not usually large enough to solve an algae problem, unfortunately. I'd look for other options as well, like GFO.

[pjf]

Thanks, Randy, but I won't let my hopes precipitate!

I have GAC & GFO in my reactor and perform a 30% water change weekly. Per the Hach PO-19 and D-D Merck kits, my phosphate levels are undetectable. Yet, I still have an algae outbreak. I suspect that the live rock or DSB in my main aquarium are the culprits.

I’ll try raising the pH and the magnesium levels next. What levels of the following parameters should I aim for?
• pH
• KH
• Mg

[Percula9]

You seem to be concentrating on PO4 alone, other nutrients like nitrate and silica also fuel nuisance algae problems. Keep doing weekly water changes and siphon detritus as much as possible. Change filter socks every 4 days or so. Reduce the light period by an hour a day may help. If a single nutrient was responsible for algae problems it would be easy to control.

[bertoni]

The algae likely are consuming any phosphate as rapidly as it is released. Often, the GFO products can outcompete a fair variety of algae, but maybe not the ones in your system.

You might try running a bit more GFO in the system. How long have GFO been used, and how much is in the reactor?

[pjf]

My algae outbreak started about 4 months ago when my skimmer’s impeller broke. It has not yet been repaired. Bubble algae, caulerpa, and bryopsis(?) are growing on the live rock. Fine “hair algae” is growing on the coralline algae on the glass.

Since my skimmer broke, 30% water changes have been performed weekly and I’ve been using a reactor with 1 cup of GFO (PhosarHC) and 3 cups of GAC (ROX 0.8). The media is replaced monthly.

Mechanical filtration is provided by my chaetomorpha, which is suspended by an upward flow. All sump water passes through the chaetomorpha, which has been growing at a healthy rate since my skimmer broke. Debris is trapped in the chaetomorpha, which is rinsed and pruned weekly during water changes.

The phosphates and silica in the system are not detectable using the Hach PO-19, D-D Merck & Salifert tests. The nitrate level is a low 0.2 ppm per the Salifert test.

I’ve tested the make-up water from my Kold Ster-il unit. Prior to adding Instant Ocean, the phosphates and nitrates in the Kold Ster-il effluent are not detectable. However, the silica level in the effluent is ~1 ppm per the Salifert test.

A few days after a water change, the silica in the system drops to undetectable levels. This occurs with or without the GFO/GAC reactor. I’m not sure if GFO absorbs silica but it is not exhausted by the silica as phosphate levels are undetectable.

Here are my hypotheses:
• There may be phosphate in my system that the Hach PO-19 and D-D Merck tests cannot detect. Perhaps these tests cannot detect phosphate levels below 0.02 ppm.
• Perhaps my daughter is overfeeding the fish. I’ve found mysis shrimp feed in my chaetomorpha.
• Perhaps phosphate binds to my live rock and aragonite sand and becomes available to algae growing on the live rock and sand.

[bertoni]

Overfeeding the fish can cause problems. Improving the skimming situation could do a lot, too.