Nitrate control in discus tank

[Luke in Phoenix]

Luke, I can tell you what mystery things are not filtered by an algae scrubber. Primarily parasites like gill and body flukes swimming around in the water column, as well as opportunistic bacteria waiting to infect damaged skin or fins. Not to mention DOCs.

I use a UV sterilizer on my tank (full sterilizer, not just as a UV filter). Super easy and takes care of all of those.

[smsimcik]

I use a UV sterilizer on my tank (full sterilizer, not just as a UV filter). Super easy and takes care of all of those.

It takes care of some of those, depending on the wattage of the sterilizer and age of the bulb. Regular water changes are the only way to keep all of the nasties diluted out of the water column.

[dspeers]

From an infectuous disease standpoint, if there are gill and/or body flukes or other parasites or viruses in the system, then there is an infected source and no ammount of water changes or UV will fix that. Needs treatment. As far as bacterial build up, UV makes more sense (indeed only with sufficient wattage and a bulb still emiting UV wavelengths) due to doubling times measured in hours rather than days, unless you are changing water daily. Also since we are talking about health and stability, evaporative losses need to replaced with RO or distilled H20 and this can be a gallon or more per day depending on the surface area of the tank, whether it is covered and the environmental relative humidity.

The conundrum I face is that if Nitrate levels trigger water changes then if you use another technique to lower Nitrates then what triggers water changes. I am curious because I plan to have planted tanks and am debating determining the proper water change frequency prior to introducing plants or just winging it with the target Nitrate max > 20 with adult discus only.

[Willie]

I am curious because I plan to have planted tanks and am debating determining the proper water change frequency prior to introducing plants or just winging it with the target Nitrate max > 20 with adult discus only.

Keep a planted tank and make large, frequent water changes.

[dspeers]

I don't disagree but as a physician, I like practice guidelines when appropriate; alternately, after 30+ years in the military, I prefer Standard Operating Procedures when appropriate. Given that, I am unsure of what is large and what is frequent, contrasted with what is possible given my disabilities. Yes I know that there a number of dependant variables but I am planning on using nitrates as a measure of adequacy when determining the frequency and volume of water changes, with plants maybe TDS is a better predictor of success (although trying to figure out what % change of source TDS should trigger a water change is a source of ambiguity as well).

Also, beautiful tank, thanks. What is your routine?

[Willie]

I do 100% water changes every other day, Don. I am retired with a large water storage tank, so this takes ~30 minutes after breakfast. Not having substrate makes this process extremely simple since a Python can clean up everything. I have only one tank left with substrate and that's going bare bottom soon.

With this kind of a water change schedule, obviously there is no nitrate accumulation nor TDS change. Both are indicators of poor water quality, but I believe they're poor indicators for making water changes. For example, medicating for high cholesterol is not a good predictor of cardiovascular success. Managing your diet to maintain low cholesterol works better. My approach is to prevent, rather than ameliorate, poor water quality.

My view comes from watching discus fry feed off the slime from their parents. Why evolve such an elaborate and energy-intensive behavior unless there's strong selective advantage to doing so? No other SA cichlids do this. In fact, at such low pH in their native environment, there's very low bacterial activity. (I can attest to this having taught graduate level microbiology courses three decades ago.) Without bacteria, there are no protozoa to feed on bacteria, no phytofauna to feed on them, and discus fry would starve if they were to browse in the detritus like other fish. I believe (no data) that discus cannot tolerate high bacterial populations which accumulate in glass tanks. Regular water changes and wiping down inside surfaces go a long way to reducing the biofilm that so many other types of fish thrive on, but discus obviously do not.

[jwcarlson]

That's a great way to put things in perspective, Willie. I know it's almost impossible to cycle a tank below a certain pH, so it would make sense that their natural habitat has a very low bacterial load. I know it's the reason honey basically won't spoil, the pH is such that nothing can really grow in it. They even use it for dressing wounds.

Anyway, I really appreciate that discussion. It would be really easy to lay back on maintenance, run into an issue, and then start blaming nitrates or something that's not really responsible.

[dspeers]

Thanks for the feedback, certainly something to think about. Does tie you to your tanks as far as scheduling, but the reasoning is sound and answers a question I had recognized but had not thought to try and resolve. Certainly the fry feeding behavior is both unusual and energy intensive and has to have a survival advantage, your explanation is excellent.