Thanks for your reply!
I have a new Eheim 4 350. Which should be sufficient for my tank.
This is an excellent filter and will provide enough
filtration capability for your tank. In any case, most of the biological "filtration" will be performed by the plants. This filter outputs a maximum flow of ~1000 l/h, which means the actual flow is going to be significantly lower due to filter media, pipes, and other inefficiencies.
In a tank with CO2, filtration is half of the story. You need to distribute CO2 all around the tank so that is consistently available to all the plants. For this you need water circulation. The guideline is a flow of ~10x the volume of tank water, i.e. 2000 l/h for your 200 l tank. Your filter is providing less than half of this. You might need to add a wave maker/power head to increase flow.
Not sure how I determine if I have enough circulation. I can see the water wrinkle on 90% of the surface.
That is a good sign for gaseous exchange! The plants (all of them) should be gently swaying, including the bottom plants.
Last night I added a skimmer (was busy with that already). It indeed removed the film from the surface!
Excellent.
Under the gravel there is 2 cm of aquasoil. I use the premium nutrition of Tropica and just dose once a week based on the recommended amount that's on the bottle.
With CO2 injection you will have to add more fertilizer than the recommended dosage, which is for tanks without CO2 injection. You should add the trace elements/micros (Tropica Premium) daily. The NPK macro nutrients (Tropica Specialized) should be added a few times per week. The actual NPK macro dosage will depend on how your plants develop. You should ask Tropica users how they are using these products and how much they are dosing in their tanks with CO2.
Note that Tropica fertilizers add a very low concentration of fertilizers to the water column and assume that you will have enough fertilizers in the soil.
Also added the drop checker and the fluid this morning was still blue. I guess I should increase the co2 supply to see if it changes.
One question about the co2: I turn on the co2 1.5 hour before lights on and 1 hour before lights off I turn it off.
It should be green when lights turn on. You will very likely have to increase injection rate. Your goal is to have a stable CO2 level from lights on to lights off. This will take time to adjust (a pH probe will help tuning CO2 - request help on this if needed). To get to a stable level, you will need to "waste" CO2, otherwise there will be fluctuations of CO2 levels, which are often a source of major headaches.
Please read this article from Dennis Wong. It provides very good input regarding <
CO2 injection>, which is complemented <
this video> and <
especially this video>.
I want to keep crystal shrimps in the tank but read that swings in co2 (and therefore in PH) can harm the shrimp. I started looking at a PH controller but would like it if I could manage to do without it. Any thoughts?
Do not add any livestock until your tank is stable. The plants will need to be growing healthy and this will take several weeks. You also do not want any livestock in the tank while adjusting CO2.
pH fluctuations do not harm livestock. Natural environments experience large pH and CO2 swings during the day. With CO2 injection and plant photosynthesis and respiration, the water will always have a daily pH and CO2 swing. Your goal with CO2 injection is actually to force a pH swing (a drop of ~1.0 pH point during the day). What you need to secure is that the CO2 concentration as measured by the drop checker is in acceptable levels, i.e. it is between green and lime green (not lime yellow). There are plenty of threads around here this topic.
The pH controller is a complicated discussion. You need to understand what the controller is actually measuring and what can influence its measurements (basically, the controller indirectly estimates CO2 based on the measurement of water's pH, while the drop checker indirectly measures dissolved CO2 - and these values can be quite different). It you use it as a plug-and-play device you might harm the livestock. You can use a controller as a safety device, but you (not the controller) should be in full control of the maximum amount of injected CO2. Again, there are plenty of threads around here this topic, but this is a rather complicated topic.
I would first start with the basics and let the tank stabilize during the next weeks while you adjust CO2, fertilizer dosage, and deal with algae and plant growth. Then we can deep dive into the other topics...