nitrate mystery????

ok, i'm confused. i thought that plants would 'eat' the nitrates that are present in a planted tank, yet i'm still getting readings of 40ppm or so the day before water change day, sometimes even a lil higher than 40. I know i'm not going to get a nitrate reading of zero, but dontcha think that is a lil high for this tank?




55 gallon tank, substrate is sand and small gravel mix. i stir up the unplanted areas during water changes, and water changes are done every 7 to 10 days and are 40% to 60% each time. any decaying plant matter is removed asap when there actually is any, which is rarely. my filters are cleaned on an as needed basis with old tank water, usually once or twice per month, and filter floss is changed out with every water change. i don't have co2 running nor do i dose any ferts. lights are on about 12 hours a day, Eclipse "daylight" florescent, wattage unknown. open topped tank. plant growth is really good, the wisteria is the newest plant in there and its grown at least three or four inches in less than two weeks.

ph is 7.8/7.9 (just tested it 2 minutes ago with both normal and high range to be sure. ph out of my tap is normally 7.8
i don't know my gh or kh - don't have the tests for those
temperature is always between 78 and 80
ammonia and nitrite always test zero
(and yes, i use an API test kit, and it is not expired)

stock:
1 large angel
1 4" albino rainbow shark, juvenile
4 emerald cories
5 long fin rosy barbs
1 unknown small striped barb
1 very small BN pleco, juvenile
4 adult brigg snails
lots of baby briggs, number unknown
a few ramshorn snails, dang hitchhikers! lol.


plants: (i think i have them all confirmed)
giant vals
huge amazon sword
medium 'rose' sword
wisteria
octopus plants
bacopa
stargrass
two types of crypts of varying sizes
one small bright green unknown rosette style plant
three marimo moss balls


filtration:
Aquaclear 110 hob, with sponge, biomax, and filter floss
Marineland Pengiun 350 dual output biowheel hob with filter floss only
(both filters have good flow and create lots of oxygen bubbles in the water and good surface agitation. water level is usually dropped an inch for clutch laying)

feeding schedule:
twice per day, but small amounts. dry prepared foods such as granules, crisps, or flake in the morning and frozen foods such as bloodworms or mysis (1 hikari cube) in the eve. snail jello every three days (1 ice cube size piece) and NLS h2o stable algae wafers every second day (but not on same day as snail jello). once in a while i will give a half dozen or so shrimp pellets for a treat for the cories.

so can anyone help me with the nitrate mystery? or is it not a mystery at all?

:feedback:

forgot to add to the feeding section, a slice of zucchini on a veggie clip every few days, and left in the tank until it is eaten up (takes about two days)

i have tested the tap for nitrates on occasion and they are always zero.

as for the thought on overfeeding, whatever food i put in is eaten within minutes by all the fish, excluding the snail jello and zucchini of course, which gets noshed on over the course of a couple days.

ok, i'm still a bit of a noob on all the various chemical names, like K, Fe, P04, etc. can you explain these for me please?

but would using ferts heighten my chances of algae? i'm loving the fact that i have none a lil too much to chance it, lol. and i really have to find out what the wattage is on my lights!