High nitrates in freshwater tank

Question
Hi Christy,
I have a 55 gal tank which has been up and running for three years.  Crystal clear water always. I have about 15 fish, for a total of about 25 to 30 inches of fish in my tank.  I vacuum the gravel of half the tank and change about 10 gallons of the water about every three months.  In the past year, I have had a growth of algae setting in.  Also, I have purchased placostamus 3 times in the last 6 months and every time they die in 2 days.  The pet store thought my PH was too low (6.8) so I started with chemicals to increase it to closer to 7.  Now, pH is better but my nitrates are way up--at the highest level (100) on my indicator card.  Why is this?  What should I do about it?  I would like to add a few more small fish to the tank but want to bring them to a good environment....Thanks, Ginger


Answer
Hi Ginger
Your tank is suffering from what's called "old tank syndrome".  Just because the water looks crystal clear, doesn't mean it's good :)  The problem is the lack of water changes.  For a normal stocked tank, I recommend changing out about 25% of the water once a week, and also vacuuming the gravel weekly.  The reason new fish are dying when you add them, they can't handle the high nitrates.  What happens with OTS, the nitrates will slowly rise, and they're not as toxic to fish as ammonia or nitrites are, so the fish adjust to the higher levels-doesn't mean it's good for them, but they adjust.  The fish keeper doesn't realize there's a problem until they add new fish and they die off quickly, or they do a large water change and it basically shocks the current fish and kills them.  I don't have any links handy at the moment, but if you do a quick search online for old tank syndrome, you can get a better understanding of what happens-ph usually drops as well, because all the elements and minerals in the water are being depleted.

What you need to do, is small water changes every few days.  I would recommend changing about 20% every other day.  Until you get the nitrates down under 20 ppm.  This will help lower the nitrates, and possible increase your ph as well depending what it is normally, but it'll do it gradually enough to not shock the current fish.

Once you get the nitrates down to under 20 ppm, I would get on a weekly schedule, vacuuming the gravel and changing out at least 25% of the water each week.  That'll help prevent that problem from happening again.

Not sure on the filtration you have, but if you only have 1 filter running, I'd suggest adding another on the tank.  All my larger tanks over 30 gallons I run 2 filters on.

One last thing, those ph up/down products....don't use them.  Most fish we buy are tank bred as opposed to being wild caught, and can handle ph ranges from 6.0-8.0 plus or minus a few, just fine.  That's one of the worst advice pet stores give out-to adjust the ph.  A stable ph is much better for fish then one that fluctuates, which is what usually happens when using those products.  Plus, that small of a difference 6.8-7.0 would not make a difference in a fish living or dying.  

Hope that helps and let me know if you have more questions.

Christy