I received the following message and thought I'd post here instead of privately for the benefit of others as well.
I have just found that my source water is high in nitrates, JDM has mentioned that you may be able to suggest a filter that removes nitrates. I think the problem is recent as the last time I checked the source water it was all in the green zone on my test strips.
Thanks in advance for your help.
I discovered quite some time ago now that I had high nitrates in my country well water. (Blood red in the API FW test making it 80+ppm)
Naturally this presents not only problems with the aquarium water, but of course with water for water changes. The solution is two pronged 1) the reduction of tank generated nitrates; and 2) A means to filter nitrates out of tap water.
To reduce tank generated nitrates:
1) feed only high quality foods as these reduce fish waste.
2) feed only once or twice a day in small amounts ensuring that all food is quickly consumed. Don't over feed.
3) Don't over stock the tank.
4) Add plants, even floating, to process ammonia and bypass the N2 cycle.
5) Consider a sand substrate. Uneaten food and detritus too easily gets down into gravel and without aggressive gravel siphoning a potential 'nitrate factory' may result. With sand, the material remains on top.
6) Consider using synthetic polymer 'scavenger' resins (e.g. Purigen) in the filter to adsorb dissolved organic compounds (preventing them from becoming nitrogenous waste).
7) Consider products like Fluval Lab Series Nitrate Remover (FNR) or API Nitra-Zorb in the filter to adsorb nitrates from the water column.
For source water, there are several options. You 'could' find other source water in your area that has lower or no nitrates. You could also purchase RO or spring water. But these could cost as much as $1/gal and there's the time and effort in hauling water.
A better approach is to filter you own water to remove nitrates. You could purchase an RO or RO/DI (reverse osmosis/de-ionized) filter. Be advised that an RO filter requires sufficient water pressure to force water through an ultra fine membrane. Most home well systems will not have sufficient pressure for this. Also, there is approximately 4 gallons of waste water for every gallon of RO water produced. Also note that RO, RO/DI, and distilled water will require adjustment for pH and the addition of minerals as alone, these waters are literally too pure for aquarium use.
API makes a Tap Water Filter that produces DI water as it trickles through a filter cartridge. Cartridge longevity depends on the source water quality, including hardness. I found that I was only able to get 50 gallons or so from a $25 filter cartridge (then have to treat for pH and minerals - I've used Seachem Neutral Regulator and Alkaline Regulator for pH and Replenish for minerals).
I also used FNR or Nitra-Zorb in a filter and spare 10g aquarium in the garage to filter water for water changes. As winter approached, I moved the process to a 29g in the basement.
I would mix the DI water 50/50 with filtered 'tap' water.
Recently I'm experimenting by using an emptied API Tap Water filter cartridge and filling it with API Nitra-Zorb. (Nitra-Zorb is regenerated with regular non-iodized table salt). This makes it a nitrate filter but doesn't strip minerals or alter pH.
It's early still but it looks encouraging. I've pulled 65g of nitrate free water through the filter so far. It will be interesting to see how many gallons before regeneration is required.
I'm also now recovering water from my basement de
humidifier, treating for pH and minerals and mixing it 50/50 with filtered water.
Although I haven't purchased one, TFK is sponsored by Aquaripure, a company the markets a de-nitrate filter. The filter promotes the culture of aerobic and anaerobic bacteria/archea (fed by alcohol or sugary solution) that oxidize nitrates producing nitrogen gas, completing the N2 cycle.
So here are some guidelines to reduce tank nitrates as well as filtering source water to remove nitrates.
One final note: With sound stocking, some careful tank maintenance and advanced filtration, you can reduce the volume of the weekly water change and still maintain very high water purity. Reducing the volume reduces the cost and inconvenience of filtered or purchased water to fight source water nitrates.
I hope this helps some folks that face this troubling problem!