Interesting water tests

I am guilty of seldom testing the water in my tanks.  Usually, if something is off I see the end result happening so I change more water and all is well again.  This Fall marks the one year anniversary of my first tropical tanks so I decided to test all fifteen this morning.
I had changed eight of them yesterday and planned to do the rest today so I was interested in what might be different with the changed vs. not changed ones.  It WAS interesting!
Of the ones I had changed, TWO had high nitrItes and all eight had pretty high nitrAtes (60 - 80 range) higher than I would have liked, except the single betta tank which had almost no nitrAtes.  
The worst one was not a surprise to me, it was my new 35 hex with the six small Angels.  I started it ten days ago and started it with used substrate and a used filter.  I only let it run for a couple of days before I added the fish but there were nitrAtes already showing on a strip test.  I know, I know, it was TOO early, but I ALWAYS have trouble with new small Angels no matter what I do so I just kept an eye on it and planned to do water changes often.  Exactly five days with the Angels in the tank I came home to find five of the six with clamped tails.  They were a bit quieter than I liked as well so as I was draining out water for a change I stuck a strip test in just to check, (I normally use the API drop tests).  It didn't have ammonia as a test but the nitrItes were up a into the caution area and it was also showing nitrAtes so I changed about 50%.  They were still eating and did liven up with the change so I did another one yesterday.  Tails were now normal again and the fish were eating like crazy starved fish.  I did use Prime so hoped they would be fine.
Their test today showed fairly high nitrItes, but no ammonia.  I didn't know if the test on that tank was reading the Prime or not so I changed 50% again today.  The other one showing nitrItes was the rainbows... for some reason although I don't think the tank is overstocked (10 dwarf rainbows and a betta in a 29g), they always seem to show nitrItes.  I did another change on that one today as well.  Both these tanks had nitrAtes in the 60 - 80 range.
Of the ones I didn't change yesterday, every single one was 0 ammonia, 0 NitrItes and <20 nitrAtes, even my heavily overstocked platy tank.  This really surprised me since ALL the tanks are fairly heavily planted with easy stuff like hornwort, water sprite and wisteria.  I do have some Amazon swords as well.
Soo, my question after all this babbling, why would a water change 24 hours earlier raise the nitrAtes OR, if they were not raised, why would some be so high while others, running exactly the same, be so much lower??  Any ideas?  Also, any clues to help lower them?  I normally do 35 -40% water change once a week.  
I don't generally use any water conditioner, (I have GREAT Well water), but do use both Seachem Flourish and Excel but only about every two weeks.  I have a minor issue with some BGA and a bit of regular hair algae, and some BBA in a few places but certainly not a major problem.  I usually just scoop out the hair algae, and break off the leaves with the BGA on them and toss them and scrape off the BBA.  Lights are Finnex FugeRay Planted + moonlights, LEDS, and run for 4 hours on am, four off midday, four on afternoon, and off for the remaining 12 hours. I did test my well water and it was 0 ammonia, 0 nitrites, 0 nitrates.

use the API test on the well water coming out.

See if you have any Nitrite readings as well as nitrate readings.

Did that, it's O, O. O. Perfect.

caoder wrote:use the API test on the well water coming out.

See if you have any Nitrite readings as well as nitrate readings.

Would have been my suggestion, Well water can sometimes get fertilizer run off.

other then that drawing a blank,

How old is the kit?

Steve

Kit is about a year old, expiration date is 2016 though. But, I have tested the well water before when it was new and it tested good then, too.
It is an artesian well so shouldn't have too much problem with run off. It does have some sort of carbon ore junk in it, but that is supposed to be safe and just a cosmetic issue with a black greasy coating settling in the pipes, etc. I asked about it being an issue with livestock/dogs/birds, etc., since we have a boarding kennel here and they assured me it wasn't and was a common issue in the area water wells.
I might still be feeding too much but the fish don't think so, besides, wouldn't that cause ammonia and nitrite issues as well???

I would have guessed the problem to be the well water also, except for your reading of 0 across the board. That really does pose a mystery. I agree that overfeeding would like give higher readings for more than just nitrates, unless your bacteria are doing such a great job breaking down the ammonia and nitrites that you don't get a reading. We'll have to think on this some more. Hopefully someone else will have an idea.

You could go with my sophisticated approach to water chemistry - do your 30% water changes every week, check tds and water hardness when you want to breed your fish, stock lightly and never buy a nitrate test kit...

I think my last ammonia/nitrite/nitrate test kit expired some time in the early 1990s. I'm no help.

GaryE wrote:You could go with my sophisticated approach to water chemistry - do your 30% water changes every week, check tds and water hardness when you want to breed your fish, stock lightly and never buy a nitrate test kit...

I think my last ammonia/nitrite/nitrate test kit expired some time in the early 1990s. I'm no help.

Well, actually, I am sort of on my way with that!  I DID test the new tank, they are new Angels and die too fast when young, at least for me, and I am still considering myself a novice... we didn't have tests back in the olden days when I did the Angels.  And, I did test Bert the Betta when he got so sick, but his were great, go figure.  But, otherwise I had to dust off the test kit before I used it yesterday since it has been collecting dust from not being used.
I will continue with my weekly water changes but maybe make myself take out a bit more in those tanks that run higher nitrates.  If I go by the behavior of the fish they are certainly doing well, in fact, my platies are doing TOO well... there are new babies in there almost daily.  I was told they kept their populations under control by eating babies???  Mine must be fussy eaters!
And, I certainly have plenty of Endler babies as well.  I HOPE none of the others decide to breed! My water is extremely hard so, with my weekly changes, they have plenty of buffers. My ph has never varied from 7.6 - 7.8.