Backyard Aquaponics
A place to discuss aquaponics

If its any consolation, neither of my RAS systems ever hit zero nitrites either. I have about twice the K1 in one I need for the amount of feed, and can never get them below .25ppm. I found a post on the earthan group site where Paul mentioned in his RAS that there was always some residual nitrites. Do other people with RAS systems achieve zero?

Paul did suggest increasing the MBBR retention time to address my issues, though because I have a combined MBBR/Sump I can't do that without reducing flow rate through the fish tanks.

Fish seem happy enough and I dose with potassium chloride to mitigate nitrite levels.

Perhaps try cleaning the shade cloth out 2 times per week and see what happens. Only change one thing at a time to be able to verify if that actually works. Otherwise you will never know what fixed the problem..

Obviously more solids/fines in the shade cloth filter will produce more ammonia. So you increase feed rate you increase TAN in the system and the biofilter needs to adapt to that new level. If you start cleaning your shade cloth at a higher frequency I would imagine your biofilter will adapt to those conditions and you would have to continue cleaning at that frequency in the future.. Or once you feel the biofilter is up to par handling the feed rate you like. Then reduce the cleaning frequency at that point to get the biofilter used to that change.. (These are just my thoughts and by no means is it intended as facts..)

Also like MattYoga said.. Longer retention time in the MBBR would probably help as well.. The way your setup is I wouldn't route any water back from the sump into the MBBR since this would increase the flow through the IBC and reduce retention time. Now if you had a separate IBC biofilter on the side (not inline) and routed some water from the sump back through that tank then you would increase retention time for that biofilter.. But I don't think you should take those steps yet. Wait this out and do what you have been doing. Slowly increase the feed and clean out your netting tank once or twice per week. Treat for nitrite should it become necessary..

Matt & Swede thanks. I do have the new line from the sump going into shade cloth/netting filter. It seemed to working great for a few days. I'm Ok with .25-.5, but I'm still getting spikes up over 1 and sometimes 2. I could add another IBC, and route the excess water that's now going into the netting/shade cloth filter(and then mbbr) into it and the retention rate for that 25-20 gpm would then be almost 10 minutes It wouldn't require any huge piping or plumbing work. I would also really like to eliminate the whole shade cloth cleaning(90 minutes is about the norm) and get a proper cone bottom and make a K1 upwelling. It would be a nightmare to replumb from what I have now, but if I could do it and not kill the fish, would probably be worth it long term.

I'm still keeping salt between 2-3 ppt. Fish seem fine, maybe I'm being too cautious??

Don't think you are being over cautious, though think you can use a lower concentration of salt to mitigate a 2ppm nitrite spike.

+1

Use a 10:1 ratio ( salt:nitrite)

It's surged higher then 1, over 2 several times. Ryan said keep between 2-3. The tilapia don't seem to care, but the koi don't like the higher nitrites.

Then stick with what he said. Just keep them alive

Look up this paper online about nitrification. By Timmons and Ebeling

Here ya go.. Couldn't link to it from my phone earlier https://ag.arizona.edu/azaqua/ista/ISTA ... erview.pdf

SORRY! Let me correct myself

Chloride to Nitrite ratio 10:1 is correct

Salinity refers to the total concentration of dissolved ions in water, the major contributors being
calcium, sodium, potassium, bicarbonate, chloride and sulfate.. That is a very different thing than dosing with chloride to 2-3ppt.. Altough that should be more than enough to prevent nitrite poisoning in fish (brown blood disease)

Thanks Swede.

How are things progressing?

Cleaned the shade cloth filter just now. Still feeding lightly, a few pounds a day max. Cool front today, water temp dropped down to about 81.

Yeah, we have been getting tempsin low to mid 60s here..