Hi Sabine,
The underwater power filter you mentioned, is it an undergravel filter? In my opinion, the best types of filters you can get are external canister filters or mounted waterfall type filters. They are much more efficient and don't heat the water up too much nor require gravel substrate.
http://www.caudata.org/cc/articles/filters.shtml
If there are excessive currents in the tank, it would be a good idea to reduce the flow by means of a spray bar, adjusting to a lower setting, diffusing with strategically placed ornaments and rocks or having the outlet against a glass wall.
Most of your regime seems fine. However, do you feed exclusively bloodworms? Also when you mentioned 2 cubes, do you refer to each axolotl or all five axolotls? It is best to feed a variety of food types to ensure optimum nutrition. Bloodworms are good but it will be better if supplemented with other food types such as live earthworms, blackworms, pellets, and occasional treats of shrimp, fish, beef heart strips etc.
http://www.caudata.org/cc/articles/foods.shtml
http://www.caudata.org/cc/articles/worms.shtml
http://www.caudata.org/cc/articles/microfoods.shtml
You will need to also check for other parameters such as ammonia, nitrites and nitrates. You want to aim for 0 ammonia and nitrites and <60 nitrates.
Floating can be a sign of stress and illness and is stressful in itself. Firstly axolotls thrive in cold water and moving it to warmer waters will only exacerbate the condition. In fact, heat stress is one of the causes of floating. Ideally, axolotls do best in temperatures around 16-18 degree celsius. Anything above 22 degree celsius for a period of time and axies will be predisposed to stress and secondary infections. What are your current water temperature? Is it stable?
Are there any other signs of illness or stress such as curled tail tip, forward facing gills, inappetance, mucus patches on skin, unusual behaviour, infections on skin or gills etc?
The best thing you can do now if you want to be safe is to fridge the sick axie.
Fridging your axie will destress it, boost its immune system and render harmful pathogens (both bacterial and fungal) less viable.
- Set your fridge to about 5 degree celsius.
- Put your axie in a container large enough to allow it to stretch its limbs and tail comfortably.
- Fill with fresh dechlorinated water enough to submerge it but not allowing it to float.
- Cover with a lid. You can use a perforated lid or netting to prevent it jumping out.
- Use a tea towel to cover it to keep the environment dark.
- Perform 100% water changes daily with clean dechlorinated water.
- You can pre prepare bottles of water in the fridge.
- Continue to offer a variety of nutritious food daily. Try live wriggly food like blackworms, bloodworms, earthworms. You can also try the usual pellet, offer treats of shrimp and fish etc. Otherwise you can also blend everything in a food processor and then roll the resultant mash into a pea sized ball to try offer your axie. Remove uneaten food within 20 min.
I would try fridging your axolotl for 2 weeks and continually monitor for improvement. Please update on the progress every couple of days.
Cheers