Phytoplankton DIY Water Chemistry Question

[Nathaniellund17]

Hello All,
Over the past few weeks I have been fighting high phosphates within my tank. I didn't think I was feeding my livestock excessive amounts of food. Then it dawned on me. Outside of frozen food and nori, the only other item I was putting in my tank was phytoplankton that I was culturing myself. I stopped dosing the phytoplankton into the tank, and my phosphates went from .24 to .02 (using Hanna checker) over the course of a few weeks. With it so low, I decided to dose phytoplankton again. I dosed about 1 to 2 cups (or about .25 - .5 liters), and my phosphates increased to .24 again the next day I checked my water. My display is 180 gallons with a 60 gallon sump.

I'm thinking it might be because of the fertilizer that I'm using in the culture - as in the phytoplankton isn't eating all of the fertilizer by the time I harvest it? I'm following the instructions of the kit to where I'm adding 2 mL of fertilizer and harvesting shortly after a week when the phytoplankton is dark green. My LFS has said you can't overdose phytoplankton, though maybe that's not the case? Any thoughts or pointers anyone has on dosing phytoplankton would be appreciated.

Here's the link to the kit that I purchase from Amazon:

Thanks,
Nate

 

[Dennis Cartier]

You might be using too much F2 for your culture. Normally the phosphate is depleted first and becomes the limiting nutrient. I would suggest filtering some of your phyto through a coffee filter and testing the clear water for phosphate. That should help determine if you have residual phosphate in the phyto, or if you are just adding too much phyto and it is being converted back into (excess) nutrients. If the latter, reduce your phyto additions. If the former, use less F2.

 

[fryman]

I have a centrifuge and have tested tetraselmis culture water for nitrate and phosphate following grow out with recommended f2 dosing. I found phosphorus dropped below detection using hanna ulr phosphorus tester after about a week (5 to 8 days), while nitrate bottomed out about 20ppm. This is using f2 from florida aqua farms.

I also sent centrifuged culture water to ICP. These results actually measured slightly elevated phos at 0.12ppm, and nitrate at 9ppm. See attached.

I dunno why there is a discrepancy. Maybe ICP is getting organic phosphorus? I haven't looked into it further.

I dose very large amounts of phyto/copepod nauplii to my tank (5-10 gallons per week). I have flame scallops and electric flame scallops and want to make sure they get plenty of food.

My display tank nitrate is pretty stable at about 10ppm, phosphate far less stable but seems to be converging at about 0.1-0.2 ppm recently. But there have been weeks I don't dose phyto and it doesn't change these numbers significantly.

 

[Pistondog]

I have a centrifuge and have tested tetraselmis culture water for nitrate and phosphate following grow out with recommended f2 dosing. I found phosphorus dropped below detection using hanna ulr phosphorus tester after about a week (5 to 8 days), while nitrate bottomed out about 20ppm. This is using f2 from florida aqua farms.

I also sent centrifuged culture water to ICP. These results actually measured slightly elevated phos at 0.12ppm, and nitrate at 9ppm. See attached.

I dunno why there is a discrepancy. Maybe ICP is getting organic phosphorus? I haven't looked into it further.

I dose very large amounts of phyto/copepod nauplii to my tank (5-10 gallons per week). I have flame scallops and electric flame scallops and want to make sure they get plenty of food.

My display tank nitrate is pretty stable at about 10ppm, phosphate far less stable but seems to be converging at about 0.1-0.2 ppm recently. But there have been weeks I don't dose phyto and it doesn't change these numbers significantly.

Do you run a skimmer?

 

[fryman]

Do you run a skimmer?

Yes I have a simplicity 240. It's turned off while dosing but runs most of the time overwise. It pulls plenty of gunk, maybe a bit more after dosing but not dramatically so.

I've read reports from people who claim dosing phyto reduces nitrate/phosphate.
I've also read reports like the OP's of dosing phyto increasing nitrate/phosphate.

In my personal experience, it doesn't matter very much. I think many people use excess f2, and this will certainly increase nitrate & phosphate.

 

[Nathaniellund17]

Thanks for the replies. After about a half a week, and not adding any phytoplankton to the tank, my phosphates are at .24 again - I checked this afternoon - making me think it's not the phytoplankton after all. I haven't checked the phytoplankton culture yet (that's a great thought on filtering out the phyto using a coffee filter.) I'm not a coffee drinker, so I'll have to go get some this week when I go to the store.

 

[Randy Holmes-Farley Verified Community Expert]

Thanks for the replies. After about a half a week, and not adding any phytoplankton to the tank, my phosphates are at .24 again - I checked this afternoon - making me think it's not the phytoplankton after all. I haven't checked the phytoplankton culture yet (that's a great thought on filtering out the phyto using a coffee filter.) I'm not a coffee drinker, so I'll have to go get some this week when I go to the store.

phosphate can be very slow to lower because there can be a huge reservoir bound to rock and sand that must be depleted as levels decline.