o out of interest (and seen lots of differing views on this) would/could Purigen make things worse?
I have been using Purigen in a few occasions. The stuff is pretty good to get a crystal clear water, and large part of the success into it is associated to its capability to kidnap organic matter in suspension. Seachem also affirms that Purigen absorbs nitrates. I have used it for both things, at different times, and really works. However, the "problem" I see with Purigen is that saturates relatively fast, so its positive effect does not last long. This means that you need to enter in the renovation cycle by using the procedure they mention, which takes practically one day of waiting (but worth doing it to save money). The time you have before saturates it depends on your levels of organic matter and nitrates, obviously. Regarding whether this is good to use or not into a lower-tech tank, the answer is "it depends". For instance, if your levels of nitrates are low, it would have a negative effect, because then it will be removing essential nutrients from water when their level is already low. Besides, degradation of organic matter in the tank also generates CO2 (whenparticles are digested by heterotrophic bacteria and microorganisms). However, if your levels are high, or you have difficulties in keeping them low, then Purigen can be used as emergency treatment to compensate this. On the other side, Purigen electrostatic capability makes me thing that probably have effect also over micro-elements, mainly cations, so perhaps have a down side in such line, especially in a low-tech with no ferts. In summary, I think if a low-tech tank works well, you do not need it. But the product will be of help if you have some specific situations. One of the cases could be the not fully well-known relationship between dissolved organic matter and algae, as it has been observed that high values of DOC are usually a triggering factor for algae. How this happens is not fully understood. ADA recommends some testing to monitor DOC and use that as indicator of algal risk. I think that is a bit an overkill (and besides, no easy testing is available, just one from ADA which is very expensive), especially because in a mature system, nitrates concentration in water will be closely related to DOC, so monitoring NO3 you have a guess of DOC levels and then, times to change water. In this context, Purigen can help, but I think that Purigen would be useful to prevent it, but not to stop it once started.
Would this not affect KH / pH though? Ie. If CO2 had reduced / been depleted that this would be reflected on measurements?
Yes, it does. In fact, pH cycle in low-tech tank is, curiosly, inverted from the one in high-tech tanks. When you inject CO2, the process is dominant controlling the concentrations of the gas. As a result of that, pH decreases during the time of the CO2 injection. There is no other way to achieve about 30 ppm of CO2, especially at kH levels a high-tech usually have. During nights, as the CO2 injection is not longer applied, pH raises by effect of the degasification process. Plants will add CO2 to water, due to breathing, but the magnitude of that is much smaller than the effect of injection, so degasification process will dominate the pH during the night, and then, raising.
On the other hand, low-tech tanks behave in all the opposite way. During the day, plants will consume the CO2 in water, what increases the pH as result of the removal of protons in the process. During nights, they stop doing so, so levels of CO2 increase and pH reduces.
The changes of pH due to CO2 injection/plant consumption have an effect in the kH, too, and hence, also in the CO2 levels reached at equilibrium point. This is related to the buffer effect of the (bi)carbonates into water and their role in the alkalinity. With pHs over 8.2, certain amount of carbonates is presented in dissolved form. When CO2 is added to water, protons are formed. With presence of dissolved carbonates, part of these protons are absorbed by CO3(2-), forming bicarbonates and avoiding a change of pH in the process. The process of dissolution of CO2 also generate bicarbonates. But CO2 in dissolved form is in chemical equilibrium with the bicarbonates concentration, which means that an increasing concentration of bicarbonates favor the increment of CO2 dissolved into water, just by mere decomposition of bicarbonates into CO2, which further removes protons of water, incrementing the buffer effect.
In the case of CO2 injection, the process is forced so no equlibrium is reached. The pumping of CO2 into water generates then continously more protons that further consume carbonates, in first place, and with pHs below 8.2 also consumes bicarbonate ions. The removal of these (bi)carbonates causes pH to reduce faster and faster, as less buffer effect takes place. This means that CO2 injection reduces kH in water, unless you had carbonated rocks to compensate the effect. There is not just this chemical process but also the active consumption of bicarbonates by the plants, which also reduces the kH value.
In the case of low-tech tanks, the absorption of bicarbonates by the plants takes also place (in fact, as mentioned, it is the main way for most aquatic plants under low CO2 conditions), and there will be also a chemical consumption, by buffer effect, at nights, when CO2 increase due to lack of CO2 consumption and increment of concentrations due to breathing. In aquariums with a few plants, the effect will be not much noticeable, especially if the water changes are regular and the kH is "renovated" somehow at this moment. But in a low-tech with a dense vegetation, the effect can be significant, and in fact, a factor to consider, as if kH drops too much, we can favor appearance of algae and difficulties in the plants to grow.
In my opinion, monitoring kH in low-tech tanks is especially important. As it is a key factor to supply of inorganic carbon to the plants, controlling the kH inside the tank and in tap water can be rather important. Tap water can also have varying kH values. Especially during summer, evaporation of the reservoirs can increase the values of kH, so it is something to consider.
Hope this answer your question.
Cheers,
Manuel
which again is going to too costly to do anytime soon. There are some non Juwel compatible lights but they are all still 45W. I have read conflicting info as to whether the unit will work with only a single tube in place (and still not sure that even if I could remove one tube how I would actually make the now empty connections watertight). Perhaps I could swap one of the tubes with a blue moonlight one (
