Nitrates and water changes
I have a 75G planted that used to be overstocked. I used to do 3 PWC a week (2 x 10% with gravel vacuum and one 30%) just to keep nitrates below 40 ppm.
Over the last few weeks, I reduced the stock to half. It now has 38 angelfish that are 6 months old.
I also reduce feedings to once a day and cut on fertilizers. Some of the plants are growing well so I trim and remove stems every few weeks.
My question is: is there another reason other than high nitrates level that I should a water change? If my nitrates are around 20 ppm, is it safe to delay the water change so I can maintain stability in the tank?
20 ppm is still high, especially with plants in the tank. My own planted tanks stay under 5 ppm (the minimum reading on the API liquid tests).
Nitrates are particularly detrimental to growing fish. For that many fish in that size aquarium, I would really do 50% weekly. May also want to consider adding more fast growing plants, floating plants are really good for that.
Fertilizer should still be used, if you starve the plants for nutrients they'll not use as much Ammonia and the bacteria will end up just producing more Nitrates. Which one do you use, and how much/often?
Increased water changes actually increases stability, rather than making the system unstable. As for your question of if there are any other reasons to do water changes, the answer is yes. Fish produce more wastes than just ammonia, for example they all release pheromones, and a water change is the only way to remove pollutants in a closed system.
Assuming your nitrates were increasing as say 1ppm/day and you were doing a 10% water change every 4 days with 0 nitrate water, then the nitrates just before the water changes would be 40ppm. After the water change 36ppm, 4 days later back up to 40ppm. The final effect of the water change is to remove the buildup beteen changes. is this case 4 days*1ppm=4 ppm. 10% change means the nitrates have to rise to 10 times the daily increase of 40ppm to reach a steady state.
value before water change=[(buildup between water change)/(fraction of water changes)] (+whatever is in replacement water).
I constantly hear that you need to do water changes to keep tanks healthy especially for those things we can't measure. I just balance out the tank with plants and top off evaporative water. And have ran tanks for up to 9 years with descendands of the original cycle fish.
With marine tanks you should maintain calcium/alk/magnesium with inexpensicve dosing, and in some tanks I did dose very low levels of iron, but overall with peat moss in the substrait my kh and gh stays constant and fish thrive for years..
I use lots of fertilizers. Flourish comprehensive 7.5 ml twice a week and Excel 7.5 ml every other day (I tried DIY CO2 but did not notice any extra growth. Excel seems to control the algae). Once in a while I pour Flourish potassium, phosphorus, nitogen, trace and iron. I also use Potassium bicarbonate (by Aquavitro) mainly to boost Kh. I have good lights but the only plant that grows like weed is a Water Sprite. I discard buckets of it to make room for my fish to swim. I think that removing plants, I remove nitrates. Am I right?
I filter aged water through peat (my tap water is a bit on a hard side) and use it to replace tank water. 25 gallons every week. I thought I can slow down if I have half the bioload.
By the way: I know you have to add fish slowly over time in a new tank. Is there anything I should watch for if I drastically reduce the stock?
Kh rises as co2 lowers. So a heavily planted tank with low co2 will have a high ph. So no need to dose potassium or sodium bicarbonate.
I do use peat but as the lower layer of the substrate. Perhaps the constant filtering of your replacement water with peat is contributing to the lower ph. I do get an initial low pH in new tanks that rises to high levels after a few weeks/months.
Yes by harvesting plants you do remove nitrates that have been converted to plant tissue. But those nitrates have already been removed from the water column. So you will not measure lower nitrates as a result.
IMHO your level of water changes is not a function of the bioload. My nitrates and phosphtes for instance are unmeasureable (after the initial cycle) with no water changes and very heavy bioloads.
Not much to worry about when reducing the bioload. In a heavly planted tank that is already blanced out, about all that would happen is the plants would grow a little slower is all.
There is a relationship between Kh, pH and the amount of dissolved CO2. The higher the Kh, the more dissolved CO2 you have (assuming the pH is the same). My pH is just under 7 in the morning. It was the carbonate hardness I was trying to boost by dosing potassium bicarbonate and general hardness to lower by filtering with peat. The tap water is quite different from my tank water, that's why I don't want to do any unnecessary water changes.
I will search "fish pheromones", I did not know fish release them too and I don't know if they are good or bad
Consider reducing further and 50% WWC at least.
I am considering reducing their number to about 10. If they will start pairing and claiming half the tank, I'll be in trouble...And that could happen in about 2 months...Meanwhile, back to changing water.
Thank you all for your reply.
My article on water changes and why they are essential will give you the background:
I realize there are still some aquarists who advocate not changing water, fine. The article cites the scientific experts and the facts are there.
Nitrates are toxic, as are ammonia and nitrite, even if less drastically so. But long-term they do impact fish health. Keeping them below 20ppm is wise, and the lower the better is always safer. Cichlids are sensitive to nitrates at 20ppm, according to Dr. Neale Monks.
On your KH, why are you trying to raise it? And what is the pH in the tank? And the tap water [remember to outgas the CO2 before testing tap water pH]? And what is the GH of the tap water and the tank water?
I may comment further with the above data to hand.
Ok, I just tested the waters. I use API test for KH/GH and nitrates and Hagen for pH (2 separate solution, one for low range and one for high range)
Tap water (aged for 3 days): pH 8, KH 6 drops, GH 9 drops
Tank water: pH 7.4, KH 3 drops, GH 7 drops
Just for fun I checked pH of the filtered trough peat water and was crazy 6 (I only passed one cup of water, hopefully is not that acid when I pour gallons at a time).
Why am I boosting the KH? I don't know. I notice that it disappear over time, I have no idea why. But it's true...Tap water has carbonates/bicarbonates, I add some and its still lower than tap. For the GH I must admit that I use some RO water in my mix....or to replace the evaporated part.
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