Designing a GFO, Phosphate, and Silicate study

[Miami Reef]

I’d like to know if phosphates read 0.15ppm and Silicate read 1.5ppm, which one would GFO remove more of?

Would phosphates or silicate bind more? Would they bind evenly? Would silicate bind more initially, then become displaced by phosphate (or vise versa?)

Can you help me design an experiment?

I have phosphate ULR testers, sodium silicate, silicate LR tester (Hanna), high capacity GFO (BRS), tank water, artificial seawater, various beaker sizes, and a magnetic stirrer. I’m sure I probably have other tools. If not, I can buy them.

How would you design an experiment? I want controls and to make it a very high-end/high quality test.


The purpose: I like to dose silicate (about 2ppm once a week) to my reef tank. I also like to use GFO for phosphate control. I don’t know if I’m wasting my GFO and silicate by using them simultaneously.

Sometimes I think about timing the GFO for the end of the week when silicate is lowest, but I’d like to know if that’s even necessary.

I use GFO sparingly (maybe once or twice a month for a few days.)

 

[Dan_P]

I’d like to know if phosphates read 0.15ppm and Silicate read 1.5ppm, which one would GFO remove more of?

Would phosphates or silicate bind more? Would they bind evenly? Would silicate bind more initially, then become displaced by phosphate (or vise versa?)

Can you help me design an experiment?

I have phosphate ULR testers, sodium silicate, silicate LR tester (Hanna), high capacity GFO (BRS), tank water, artificial seawater, various beaker sizes, and a magnetic stirrer. I’m sure I probably have other tools. If not, I can buy them.

How would you design an experiment? I want controls and to make it a very high-end/high quality test.


The purpose: I like to dose silicate (about 2ppm once a week) to my reef tank. I also like to use GFO for phosphate control. I don’t know if I’m wasting my GFO and silicate by using them simultaneously.

Sometimes I think about timing the GFO for the end of the week when silicate is lowest, but I’d like to know if that’s even necessary.

I use GFO sparingly (maybe once or twice a month for a few days.)

Cool! Here is an idea.

To get your feet wet you can do this offline in Instant Ocean or salt of your choice, and/or a sample aquarium water if you suspect it contains something that could affect GFO binding of these chemical species. The simplest setup is to gently magnetically stir the saltwater-GFO mixture in a beaker or any clean container. You will probably need to filter samples for testing because GFO will likely crumble. You might prevent this by placing the stir bar in a shallow container that is not much wider than the stir bar resting on the bottom of the beaker. A 0.45 μ filter should work to remove the GFO dust though it will become clogged if you don’t let the sample settle out first. Consider taking measurements every hour when first starting out to get a sense of how quickly each chemical species is binding. Starting with a liter of water will allow multiple samples to be removed without greatly impacting the GFO to water volume ratio.

 

[Miami Reef]

Cool! Here is an idea.

To get your feet wet you can do this offline in Instant Ocean or salt of your choice, and/or a sample aquarium water if you suspect it contains something that could affect GFO binding of these chemical species. The simplest setup is to gently magnetically stir the saltwater-GFO mixture in a beaker or any clean container. You will probably need to filter samples for testing because GFO will likely crumble. You might prevent this by placing the stir bar in a shallow container that is not much wider than the stir bar resting on the bottom of the beaker. A 0.45 μ filter should work to remove the GFO dust though it will become clogged if you don’t let the sample settle out first. Consider taking measurements every hour when first starting out to get a sense of how quickly each chemical species is binding. Starting with a liter of water will allow multiple samples to be removed without greatly impacting the GFO to water volume ratio.

Thanks! I have 0.45um syringe filters.

What about the controls?

How do I know how much GFO to use in the beaker?

I have various sizes of beakers, so I can definitely put the stir bar in a small beaker inside the 1L beaker.


What do you mean by, “you can do this offline?”

 

[rishma]

A little thread side track if you don’t mind…why and how (assume sodium silicate) do you dose silicate? I recall Randy saying he liked dosing it for sponge growth. I’ve never given it much thought.

As far as the experiment goes, have you already done it empirically? You must see something that makes you wonder. It seems like you could get a pretty good idea by measuring your tank before putting in GFO, then doing a bunch of tests and watch them drop. Then stabilize the silicate and phosphate back at the starting levels and repeat without GFO. Not very sophisticated, but honestly my tank is my favorite laboratory.

Part of my thinking is there are always things going on in the tank biologically that I don’t understand. While it lacks control, in the end if I know learn something, it’s applicable.

 

[Dan_P]

Thanks! I have 0.45um syringe filters.

What about the controls?

How do I know how much GFO to use in the beaker?

I have various sizes of beakers, so I can definitely put the stir bar in a small beaker inside the 1L beaker.


What do you mean by, “you can do this offline?”

By “offline” I just meant doing it outside the aquarium GFO reactor which is inline with your systems water treatment equipment.

A control design relates to the question you are asking. For discussion purposes lets assume the question is whether the rate of adsorption (rate could be mg of species per g of GFO or mg of species per g of GFO per hour) of silicate and phosphate are different AND whether the presence of one affects the rate of the other. A refinement of this question would add “and does the presence of dissolved organic material in aquarium water affect the adsorption of either species?”. Here are some control ideas.

Compare rates of chemical species depletion individually and together with a fixed amount of GFO ( not investigating the effect of the amount of GFO nor the capacity for each species)

1 liter of Instant Ocean plus

Control 1) Silicate added to 1.5 ppm
Control 2) Phosphate added to 0.15 ppm
Treatment: silicate added to 1.5 ppm and phosphate added to 0.15 ppm

Measure solution concentrations
Add GFO to controls and treatment. The amount must be the same for all. How much might be calculated relative to the maximum amount of phosphate 1 g will hold, or some small amount so the adsorption does not occur before the first measurement. The rate also will depend on the stirring speed. I would guess that 1 gram or 1-5 mL might be a useful starting point. A systematic approach would be to conduct a small number if experiments, say 3, looking at how fast phosphate is removed from 1 liter of Instant Ocean with 1, 4, and 8 g or mL of GFO
Begin stirring
Initial measurement points could be 30 minutes, 1, 2, and 4 hours. Based on results of these, space additional collection data points accordingly. Collecting data at 24 hours is a good way to ensure the adsorption has stopped.

The controls and treatment do not have to be performed at the same time.

Make sense?

 

[Randy Holmes-Farley]

A very interesting and useful test, with some complications. Just a quick set of comments before I think about this more later...

1. What initially binds and what stays stuck in the presence of the other ion may be different. They can swap places between water and bound.

2. Organics in tank water may partially block both, but I do not know the extent or timing of this.

3. Chemical binding to surfaces is related to the amount in the water. Thus, the absolute and relative concentrations of silicate and phosphate are important.

4. pH will matter. It changes the GFO surface and the relative amounts of silicate vs silicic acid and the several forms of phosphate.

5. The amount of total binding will obviously be determined by the amount of GFO, and if at low GFO levels, most sites are occupied, the relative amounts bound will be different than when there is a lot of GFO and an excess of sites available so that one of the ions in the water begins to run out.

 

[Miami Reef]

A little thread side track if you don’t mind…why and how (assume sodium silicate) do you dose silicate? I recall Randy saying he liked dosing it for sponge growth. I’ve never given it much thought.

Dosing silicate is very important to me.

Silicate grows sponges and diatoms in tank.

The sponges look cool and make my rocks rich with life. I like the way the bright, yellow sponges nestle in the rocks.

The sponge feeds my linkia starfish, which I believe is the reason I’ve been keeping it alive for over 2 years so far.

Silicate grows diatoms which I believe can feed corals when you scrape the glass. It also is food for filter feeders. The main diet of copepods are diatoms, so their population will increase by silicate dosing.

 

[rishma]

Dosing silicate is very important to me.

Silicate grows sponges and diatoms in tank.

The sponges look cool and make my rocks rich with life. I like the way the bright, yellow sponges nestle in the rocks.

The sponge feeds my linkia starfish, which I believe is the reason I’ve been keeping it alive for over 2 years so far.

Silicate grows diatoms which I believe can feed corals when you scrape the glass. It also is food for filter feeders. The main diet of copepods are diatoms, so their population will increase by silicate dosing.

That’s a convincing set of reasons. I’ll look into a diy silicate dosing solution because I need another thing to tinker with. :).

Next I’ll be asking Randy if I can just put silicates in my kalk and he’ll ban me from the forum lol

 

[Randy Holmes-Farley]

That’s a convincing set of reasons. I’ll look into a diy silicate dosing solution because I need another thing to tinker with. :).

Next I’ll be asking Randy if I can just put silicates in my kalk and he’ll ban me from the forum lol

I think the solubility of calcium silicate would be too limiting to be very useful, unless the desired silicate was pretty low. lol

 

[Randy Holmes-Farley]

I think the suggestions so far sound good.

I'd pick a GFO amount simply by scaling down from tank use. How much GFO per gallon in your tank, same in the test.

I also agree that having it loose is fine. But you don't want to pulverize it as that may expose extra surface area. Largish GFO pieces sitting on the bottom and water slowly moving over it is good enough.

The first few tries will have to just be trial runs to see what happens and if you need to change times, amounts, whatever.

 

[SomeHappyFish]

A very interesting study ! Hope to know more :)

 

[Randy Holmes-Farley]

FWIW, when I was testing the reversibility of phosphate binding to GFO many years ago (to dispute manufacturer claims of it being irreversible), I used a very small filtering device. I think it was like this one from amazon. Put the GFO in a media bag that can hold it, and pack it in such that the particles don't tumble around.