Phosphate reduction help needed.

Sordfish · Oct 9, 2023

I am trying to get my water chemistry right. A month ago my nitrates were at 13 and my phosphates were 0.03. 2 weeks ago my nitrates were at 10 and my phosphates were at 0.17. At that point I had a lot of hair and turf algae on 3 of my smaller rocks. I manually got rid of 90% of the algae. I have been testing every other day while removing the algae. Currently my nitrates are at 3.9 and my phosphates are at 0.31.

1. I would have expected both NO3 and po4 to go up given the algae removal. However NO3 went down, while PO4 went up. Does any one have an explanation for this? I have a roller mat and a skimmer which is skimming dry but well. I feed pellets through an auto feeder twice a day and frozen food by hand once a day. Nothing changed in any of these aspects of the tank.

2. I am going to try to lower my PO4. I have both tropic Marin np eliminate (carbon dosing) and rowaphos. In this case I am leaning toward rowaphos since NO3 is not high. Any thoughts?

3. If I use rowaphos I’ll simply put it in a bag and put it in my sump - I do not have a reactor, and prefer not to incur any further expenses right now. Any issues with this - besides not being optimal?

4. Which chamber in the sump should I put it in. I do not have filter socks - use a roller mat - so that is not an option. I can put it in the return pump chamber or the chamber before that which is meant for a Refugio but is empty.

Thanks

Pistondog · Oct 9, 2023

I'd put the gfo in the chamber that is most turbulent

Randy Holmes-Farley · Oct 10, 2023

I would not spend time trying to explain why nutrients moved as they appeared to, in part because it might just be random test error, and partly because there are many factors that could explain it, but you won't know with any certainty what did it.

Reducing phosphate is a fien plan, but don't expect it will necessarily help with algae until you drop it low enough that some corals may also be limited by it.

Rowaphos in a bag will not be very effective, but it's a fine thing to try. You want the most flow through it you can get.

jda · Oct 10, 2023

If you are set on GFO, you need to use it quickly and efficiently. It can quickly develop film bacteria on it and then nothing will bind to it. Reactor with a gentle tumble will usually exhaust the GFO in a day, or so... so use a small amount and replace it often. GFO in a bag is not very effective, like others have said. Always replace your GFO before you change water since it will release po4 if the water column level gets lower.

Biological control of po4 is mostly ineffective, IME. Carbon dosing works way better to lower nitrate and fuge/chaeto is better at maintaining than lowering, but they can lower over longer periods of time... so can skimming more. Chemicals and media are better for faster reduction of po4.

Algae can do very well with other types of phosphorous that you cannot test for and also very low po4 levels. My tank has between 1-3 ppb of po4 and I have chaeto in a fuge that grows like crazy and my display would be overrun with hair algae if I did not have many urchins and snails.

Sordfish · Oct 18, 2023

jda said:
If you are set on GFO, you need to use it quickly and efficiently. It can quickly develop film bacteria on it and then nothing will bind to it. Reactor with a gentle tumble will usually exhaust the GFO in a day, or so... so use a small amount and replace it often. GFO in a bag is not very effective, like others have said. Always replace your GFO before you change water since it will release po4 if the water column level gets lower.

Biological control of po4 is mostly ineffective, IME. Carbon dosing works way better to lower nitrate and fuge/chaeto is better at maintaining than lowering, but they can lower over longer periods of time... so can skimming more. Chemicals and media are better for faster reduction of po4.

Algae can do very well with other types of phosphorous that you cannot test for and also very low po4 levels. My tank has between 1-3 ppb of po4 and I have chaeto in a fuge that grows like crazy and my display would be overrun with hair algae if I did not have many urchins and snails.

Thanks for the replies. This was very useful. I just wanted to post my results in case someone comes across this in the future.

I added rowaphos bags into the baffle separating the return chamber from the previous one. I placed it over the sponge which resides in that chamber. I used 100g in my first application. The tank is 120g in total volume. Gfo was used up in 6 days - the phosphate measurements went down from 0.3 to 1.2 and then back up to 0.2. At that point I replaced it with another 200g bag. Now, 2 days later my phosphate is at 0.04, which is perfect.

My skimming is maximized with the skimmer I have. I did add some more cleanup crew and I’ll see whether they are able to keep the algae at bay, now that I have removed most by hand. My plan is to set up a fuge but I do not have any macro algae yet. I’ll get some this weekend.

I guess my next question is whether to always keep gfo in the sump, or simply add it as needed. I.e. should I remove it now?

jda · Oct 18, 2023

GFO can get coated in organic film and not work anymore. If you just toss some in the sump, it might bind some po4 for a bit, but then probably quickly just do nothing.

Sordfish · Oct 18, 2023

jda said:
GFO can get coated in organic film and not work anymore. If you just toss some in the sump, it might bind some po4 for a bit, but then probably quickly just do nothing.

Thanks. So would the appropriate thing to do be to set up a reactor this weekend, along with the fuge? Or now that the p04 is in the desired range just use go as needed from time to time. I was just trying to understand whether gfo is treated like dosing (more like reverse dosing really) where you keep gfo at all times to remove a certain amount of po4 every day. Or whether it is to be treated as an emergency treatment only.

jda · Oct 18, 2023

GFO will bind as much as it can as quickly as it can. You can use it regularly, just use small amounts and change it out quickly. This is the best way not to waste any, IMO.