Nitrate Level High, Advice Please,

[DaveA76]

hi, just changed over to malawi as have a high ph and hardness in the area and got fed up with trying to bring it down so matched the fish to the water, now the tank has always been well stocked so the filters are used to a high bioload but my nitrates have always been 10 - 20 ppm, started the changeover 10 days ago so at no point has the tank been empty to let the filters die off, but i have done a lot of rescaping so stuffs been stirred up but have done around 25% water change every rescape and when adding rocks to clean all the loose waste up so probably 5 time in the last 10 days, all the malawis in there now are between 1 inch and 2.5 inch of which there are 20
thinking of putting another external on to over filter a bit more, would this help bring nitrates down ?
 
 
 
tank 55gal 4 foot fluval roma
filers, fluval 305 and fluval 3+ so output is about 1700 lph which is 7 x turnover
real plants are vallis and anubias, rest are silk
bogwood at one end but not lowering ph 

 
heres the tank stats at the moment after just doing a 25% water change
 
water stats are using api freshwater test kit
gh             12
kh             11
ph               8
nitrite           0
ammonia     0
nitrates        40 -80 cant tell both look same on test card out of the tap 5ppm

 

[Mamashack]

The quickest way to bring the nitrates down is water changes. Adding a filter won't affect the nitrate level unless you add nitrate-reducing chemicals, but that shouldn't be necessary if you are doing regular water changes. Another way is to plant heavily, but that would be slower than water changing and more a long term solution.
How often do you test for nitrates and then what % and how often do you do water changes usually?

 

[DaveA76]

Used to do 25% a week but been doing more this week with the tank rescape will do a 50% tonight and see if it cimes down any

 

[DaveA76]

50% tonight and nitrates down to 20ppm so thing ive done it also bought another external today a 306 fluval so will have good turnover now

 

[DrRob]

What you're seeing is an active biofilter doing it's job and sending the waste through the cycle into nitrate effectively. The levels you have are fine, they won't cause any trouble, however they're a sign that there's a lot of bioload active in the tank, common in malawi set ups, which will be driving up invisible things that you can't test for.
 
As you're already discovered, upping the water changes gets the nitrate levels down, but it also removes the other things that you can't see, so it's really the best way forward. Large is better than frequent for removing things, unless the frequent is very frequent.

 

[VTDrew]

Water change slowly.  Fish are just as sensitive to filthy water as they are clean.  If your levels have been high for a long time, you want to bring it down gently over a few days or weeks.  60/80 is nothing to completely freak about, yeah, its not clean, but its not deadly.

 

[DaveA76]

thank everyone i just want them to be happy and healthy