Guys, just had a major development with this.
I was due to do a PWC
today; and as each of the last 3 waterchanges I've done have resulted in fish deaths, I decided to do a thorough test on the PWC
water before I put it in (as opposed to the normal temp/pH/SG
checks I usually do); yes I know I should have done this sooner, but this was the last thing I was expecting:
The new water has 1-2 nitrite in it, which I guess could be immediately toxic (death within 30mins-1hr) before it's mixed properly in the tank (approx 25% changed). I've tested this twice, and compared with a sample from my tank (0, ever so slightly pink as per test strip). Now, here's the strange thing: I've tested my RO
water (made freshly yesterday, tested 001TDS) and the nitrite in this is completely clear (i.e. 0). No ammonia, by the way.
So, it looks like this is coming from the salt. This is Seachem ReefSalt. BUT, I used a brand new bag of salt for this as I was wondering if it was the salt that was the problem. I bought the two bags a month apart, from different sellers, so it'd be very coincidental that both bags have major problems and include nitrites; I've always used this salt without issue for the past 6 years.
I wonder if there's another explanation: bucket, powerhead, thermometer etc. I use that's got gunge built up inside it or something; could this cause nitrite to leech into the water? If not, is there anything else that could cause nitrite to develop, e.g. airborne or any other factors?
Hope to get to the bottom of this! I'm glad I've found this, as this was really questioning my interest in the hobby.
UPDATE: I've just tested a cup of RO
water with a few spoonfuls of salt in it, and again this is showing 0. This wasn't even at the correct ratio/SG
, or fully mixed (much more salt than normal, i.e. off the scale, just tested it out of interest). So, it looks like it's not the salt either.
I'm now going to mix just RO
water (no salt) in my bucket as normal for the next 24 hours, and test it at different intervals to see how the nitrites change. I'll keep you updated...