Dead fishs

Question
I had asked about two weeks ago about a 10 year plus Pelco that died with a white film.  I figured it was old age.  Also had 5 healthy bala sharks.  

I had taken the water to be tested by a reputable pet shop, and they said everything was good but the nitrates were high.  They suggested I do a water change and have it retested, before adding another Pleco.  I did that, and took a sample for retest.  Different store person tested it and said nitrates were still a little high, but should be OK for new fish.    

So my son picked out this white bottlebrush Pleco, about 5 inches long, for $30.00..  That was 2 June, I added it to the tank.  It seemed healthy, but spent most of the time inside a castle, and came out at night.  The pet store sold me algae wafers to add once a week.  Did that the first night, and the wafer was gone, in the AM.  Few days later I dropped one in with the tank light on.  The bala sharks devoured the algae wafer.  So don't know who ate the first one..

I fed the fish yesterday AM, 13 June.  Everything seemed healthy.  Than about noon I found the largest bala shark, about 4 inches long stuck on the Marineland Emperor filter.  (25 gallon tank).  Than about an hour later found another bala shark dead.  So put that one in a baggy, and took it to the pet shop, with some water.  They said it looked healthly, maybe a couple red streaks, but looked normal.  They tested the water they said the nitrites were a a little higher than before, but nothing that would kill a fish.  I noticed after the last water change, a couple days later I had brown (algae) on top of the castle, and a shell in the tank.  They said that was probably why the nitrates were high, and just brush that off, and it would eventually work out of the tank, from water changes.  I had been leaving the lights on longer since adding live plants, maybe 3 weeks ago.   They said do another change of water next week, and make sure my tank water temp was 80 or 82 degrees.  It was around 76 degrees.  They said the 76 degrees might be stressing the fish.

So got home, and the bottlebrush (30.00) Pleco was dead.  Than an hour later another bala shark, and by morning the rest of them were dead.  

Don't know what went wrong...  The tank was set up in 1991, and I have never had a problem.  I live in Florida, and with evaportation, I seem to add a gallon of preboiled water every two week, than vacumn the gravel and replace 1/4 of the water each month.

The tank is a 25 gallon antique my grandfather used to own.  Brass and glass trim, with a slate base.  So would like to keep that tank working.

Can you give me some advice?  The gravel in the tank has been in the tank for maybe 12 years..  I'm thinking of cleaning the tank, testing and maybe sealing if it leaks, and replacing the gravel, with brand new gravel from the store.  I read on the internet that bacteria is beneficial for a tank, and maybe it would be better to keep the old gravel..?  Old Tank syndrome vs New tank syndrome...

I plan to replace the Marineland Emperor 400 filter with a brand new unit, just in case there is a filter flow problem.  That's maybe 7 years old filtering unit.  Plan to clean and set up the tank next week, and will be on vacation until around 20 July (about 4 weeks) before adding any new fish.

Any advice you could give would be greatly appreciated!

Thanks, for your last response.

Answer
Hi Art;

I am so sorry you lost your fish. What a shame.

I see nothing wrong with the tank, gravel, temperature or the filter system you have. There may be some confusion at the fish store between nitrAtes and nitrItes though.

Nitrites are highly toxic. If you have any level of it registering on a test in an established tank, do not add new fish. Elevated nitrites means there is excess waste in the tank somewhere. The gravel needs to be vacuumed and 25% of the water changed at the same time when this happens. Do the vacuuming and 25% water change twice a week until everything becomes normal again.

The same amount of water changes (25%) along with gravel vacuuming should be done every week to two weeks as part of a regular maintenance schedule. Once a month is just not enough. These regular changes lowers nitrate, which is present in all established aquariums, but should be kept at 40 ppm or lower. It is relatively low in toxicity, but if allowed to stay over 40 ppm the fish will stop breeding, stop growing and become ill quite easily.

Bala Sharks are really too big a fish for the 25 gallon. They get to be over a foot long and are very hyper. Better choices are fish like tetras, platies, swordtails, dwarf gouramis, danios, etc.

Followups welcome

At Your Service;
Chris Robbins

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