[madcrafted]

I don't really have a dog in the fight here since I mainly keep shrimps but I do know for a fact that the species I keep don't tolerate nitrate levels over 10 ppm very well, with 20 ppm being fatal sooner than later. It is for the very reasons stated earlier by @Discusluv about weakening the immune system. Bacterial infections are very common with these types of shrimp. Temperature also plays a significant role in all of this. If one were to keep temperature cool, maybe these detrimental strains of bacteria would stay dormant and never become a problem? I certainly wouldn't bank on that though. I'd rather just raise healthy shrimp and not worry over it. I'm not saying 20-30 ppm is all that high either but it is in my case.

My betta/amano shrimp tank is a different story all together. I often see red API samples in that tank. My guess is between 40-80 ppm. I don't dose nitrates in that tank since quitting CO2 and running it low tech. The bioload itself provides more than enough "organic" nitrogen. I'm already doing weekly 50% WC as it is. I don't care to do more than that, so I don't. Everyone seems fine and plants are growing great. Having said that, these aren't levels I would aim for. I'd probably stick to 10-20 ppm if I had a choice (without frequent water changes that is).

Many of us have gotten away with high nitrates for various lengths of time, so we tend to repeat what works, regardless of it being "ideal".

 

[madcrafted]

What I found interesting in one of those articles was the mention of freshwater species being more sensitive to nitrate levels than saltwater species. It's common practice for the saltwater folks to use denitrator units or natural nitrate reduction filtration (NNR) with live rocks and sand to keep nitrate levels down. Then you have the planted tank folks (myself included) that have dumped KNO3 in their tanks like it's going out of style.

I've started PPS dosing around the time Dennis posted all those beautiful pictures of his tanks using the PPS method of dosing. So far, it's been working really well for me on a majority of my tanks. It's just a shame I can't get the nitrates down in my betta tank. I think it's suffering from old tank syndrome or something. Maybe the purigen pouch needs recharging, it's been about 6 months since the last refreshing. Could be all those damn mulberry leaves breaking down also. I keep one in there almost everyday now. I had to do something, the amano shrimp were eating my healthy lobelia cardinalis to nubs. lol

 

[madcrafted]

I'm having a hard time believing that nitrates are the reason for the OP's deaths, especially dosing PPS. Granted, they are high and should be reduced. There has to be something else going on. Maybe a temporary ammonia spike, insufficient O2 levels, parasitic/bacterial infection (maybe carried over from LFS even). The fact that so many have raised livestock with EI dosing makes me skeptical about nitrates being a cause. I'd look elsewhere for your issue.