What nutrient levels for macroalgaes?

[ChrisC1029]

I'm thinking about adding macroalgae to a refugium, largely for nutrient export. I'm currnetly running with nitrates that are less than 1 ppm, silicates undetectable, but with somewhat elevated phosphates in the range of 0.05-0.125 ppm. Are there (and I assume there are) minimum levels of nutrients required to promote the growth of macroalgae, and does anyone know what they are? How about iron and iodine?:spin2:

 

[tapper of spines]

Iron is needed for the production of chlorophyl, and so supplementing that is often done. I don't believe that plants need iodine, but I could be incorrect.

HTH,
TOS

 

[Frick-n-Frags]

I have the best luck with macros when NO3 = 0 and PO4 = 0. Those basically grow microalgae on top of the macros.

I supplement a lot of Iron+Mn and I use our tapwater from lake Erie, very hard, very unpolluted with fertilizers and heavy metals, etc to also supplement light metals.(it was originally for the corals)
but seems good for the macros too.

 

[ChrisC1029]

Frick-n-Frags:
Interesting, I've assumed that to grow macroalgaes you need some nitrate and phosphate in the bulkwater. Have you measured nitrates and phosphates in your Lake Erie tap water? Could it be that there are nitrates and phosphates there but your macros strip them very quickly from the bulk water in your system? Or am I wrong in assuming that macros need some nitrates and phosphates, although if thats true I can't understand why people grow them for nutrient export.

 

[Frick-n-Frags]

Whatever fertilizer there is, I assume gets quickly used up by my mass of algae because my water has read zeros across the boards for years now, even though I periodically get cyano outbreaks. I think the algae just matches the fertilizer input and as long as i aggressively harvest, I don't think it ever makes it back into the water.

 

[tapper of spines]

I just looked it up in Tullock's book, "Natural Reef Aquariums." He claims that iodine is essential for the growth of macroalgaes.

HTH
TOS

 

[Frick-n-Frags]

Whew, good thing I dose it. Actually, I have been dosing it for my Xenia and gorgonians, but if the plants use it too, bonus.

I actually got the water assay from the water department which had the pollutant/mineral breakdown in parts per BILLION. There was almost no BS in that water especially fertilizers and heavy metals. (God help you if you stir the muck on the bottom, Lake Erie has an evil past but sedimentation and zebra mussels have made it all different now )

personally, I think there is a little extra something in the water in early fall but overall I have run my reef for 15 years on that water with no complaints. I have my nice RO unit still ready to go......

 

[ChrisC1029]

Yeah, I thought I saw somewhere that iodine was needed, but I couldn't remember where. Another thought occured to me. Perhaps the macroalgae aren't getting all their nutrients from the bulk water, but some is coming from the substate (at least for those that are attached to sediment/ live rock). Allthough I thought I read somewhere that macroalgae don't absorb through their "holdfasts". So maybe that applies only to true plants such as grasses and mangroves. Man, I need to get a good book on macroalgaes. Anyone know one?

 

[Randy Holmes-Farley]

I don't believe that plants need iodine, but I could be incorrect.

The literature says that it is required for growth by some algae and not by others. THey all take up a lot of iodine, but some more than others. Some get up to almost 1% by dry weight iodine!

The follow up is whether any or all get enough naturally in our tanks, or whether supplementing them helps.

I'm testing the hypothesis on Chaetomorpha and Caulerpa racemosa right now. The results will publish over the next few months.

FWIW, Chaetomorpha in my tests grew 4-6 X in weight in only 10 days!! They had about 4 ppm nitrate, 0.06 ppm phosphate, and +/- 0.05 ppm iodide on top of whatever is in IO salt mix that has been in a test tank (with feeding and macroalgae growth) for about a month.

 

[mogurnda]

NO3 PO4

NO3 PO4

Seems like it depends on the macroalgae. According to AlgaeBase (and my own polluted tank) Ulva needs relatively high nutrient levels. Probably why it doesn't fare well in reefs with no detectable nitrate.